New NMR Approaches For Studying Battery Materials and

Fast Ionic Conductors

Julien Breger, Meng Jiang, Young Joo Lee, Wonsub Yoon, Namjum Kim, Francis Wang,

John Palumbo and Clare P. Grey

SUNY Stony Brook

Introduction Part I: BatteriesHow do rechargeable batteries work? What are some of the technological requirements for 21st century devices?Where are some of the fundamental scientific breakthroughs required to

achieve these goals?What “New” approaches can be used to investigate Li-ion battery materials?Introduction to NMRApplication to spinels and layered materials

Part II: Ionic ConductorsMechanisms for ionic conduction in solids Devices that require rapid ionic conductivityStudying motion by NMRApplications to Aurivillius phases

Part I. Rechargeable Batteries: Applications and Demands

Portable (electronic) technologies have created an increasingly high demand for batteries that last considerably longer and deliver power faster are non-toxic and may be readily recycled are cheaper and much lighter..

Applications include: Electric and Hybrid Electric Vehicles (EVs and HEVs) Golf carts, wheel chairs and industrial vehicles Laptops Cell-phones digital cameras Camcorders, portable tools Artificial hearts (current battery lasts 4 hours!) memory backup, energy storage, generators, power for remote locations...

Different Applications Have Very Different Power Requirements

Portable Electronics (Cell phones, laptops, PDA, digital cameras)

Medical Devices

Portable tools

Back-up power (UPS)

EVs and HEVs

Electric bikes/scooters

“Industrial” EV, forklifts,

golf carts

Low Power

(high energy)

High Power

Power Storage for Renewable Energy

Batteries come in two types:

Primary: discharged once and discarded - lower energy/capacity applications

Secondary: rechargeable and can be used over again (e.g., Ni/Cad), rocking chair batteries

Li (anode)

-MnO2 (cathode)

Separator (electrolyte)

Li/MnO2 bobbin cell

Chemistry is not reversible

Charge

DischargeLi+

Li+

Anode: Graphite LixC

Cathode: LiCoO23 V

What is in a battery?

The Ni/Cd or NiCad Rechargeable Cell

Negative electrode Electrolyte Positive electrode (anode) (aqueous) (cathode)

Cd0 + 2OH- Ni3+OOH + H2O + e-

--> Cd2+(OH)2 + 2e- --> OH- + Ni2+(OH)2

OH- ions released at the

cathode travel to the anodewhere they react with the 1.35V Cell

Cd metal. I.e., electrolyte must allowionic but not electric conduction

Difference in the

couples (reduction potentials) of the two 1/2 cells determines the cell voltage

Cd NiOOH

OH-

e-

What is required to build a rechargeable battery?

Design a cell in which the chemistry is reversible over many cyclese.g., the lead acid (car) battery:

(Pb0 + Pb4+O2 + H2SO4 -> 2Pb2+SO4 + 2H2O) 2V

Requirements: large differences in the potentials of the half cells (i.e., Pb4+/Pb2+ and Pb2+/Pb0

=> High voltages Light materials => High energy densities An electrolyte that does not react with the anode or the cathode (under as

wide as possible temperature range) An electrolyte with high ionic conductivity Allows rapid discharge Conducting anodes and cathodes => (and charge)

(Allows current to be removed) I.e., high power densities Non-toxic materials Stable in charged and uncharged states H2 evolution; unstable in

discharged state

Much higher voltages may be achieved with Li-ion batteries

In theory, a more than 2V gain in voltage can be achieved with a Li+/Li anode

Li is also v. light ---> higher energy densities Some electrochemistry: E0 (V)

Li+(aq) + e- -> Li (s) -3.04PbSO4(s) + 2e- -> Pb(s) + SO4

2-(aq) -0.36

Cd(OH)2 + 2e- -> Cd(s) -0.824

[Cd2+(aq) + 2e- -> Cd(s) -0.402]2H+(aq) + 2e- -> H2

0

J. -M. TarasconNature ‘01

but….E.g., LiTiS2 ----> TiS2 + Li

Whittingham et al. ‘72

The big advance in this field came with the development of the SONY “Rocking-Chair”

battery in 1990

LiCoO2, J. Goodenough (1980) 2ndary host material, Murphy et al., and Scrosati et al. (‘78 and ‘80)

Lithium shuttles backwards between two layered compounds Very high voltage (4 V; cf Ni/Cd @ 1.35 V)

Solid state chemistry at the cathode end...

LiO

Co3+ is oxidized to Co4+ on Li removal (deintercalation) I.e., during charging

volt

age v

s. L

i/Li

+

Polymer Binder

Carbon black

Positive Electrode

Ohzuku et al. J. Electrochem Soc. 140, 1862, ‘93

Co

IntercalationOxide

And at the anode end..

Graphite anode forms an intercalation compound LixC

Charging

Energy density Cycle Life Voltage

SONY Cell 90 Wh/kg 500-1000 4V

Pb acid 30 250-500 2V

Ni/Cd 30-35 300-7001.3V

Ni metal hydride 50 300-6001.2V

Tarascon Nature, ‘01

Energy density (Whkg-1)

Co is toxic and expensive Not sufficient Co globally to meet perceived

demands for rechargeables Only 0.5 of the Li can be removed. I.e., low capacity V. slow to charge and discharge (low power) - not suitable for

E.V.s, H.E.V.s or other high power applications

Why is more research needed?Some disadvantages of the LiCoO2 cell

- Li

What is motivating all this work?New markets for Li

Power tools

Bosch, Makita, Cooper, Milwaukee, Metabo all have high end powertools with Li-ion batteries spinels

Hybrid VehiclesCurrently all NiMH

Clearly effort to go to Li-ion (e.g., Toyota, Johnson Controls, Samsung)

Conservative estimate of 3.5% HEV market penetration in 2010 requires 1 Million KWh of battery capacity.$1-3 Billion dollar market

Power back-up (small and large)

Already happening

Future market?

Soon to come?

A Large Growth is Predicted for the Li-ion Battery Technology - which will be driven by

improvements in performance

Ni-Cd Ni-MH Li-ion

$1 Billion $0.6 Billion $4 BillionMarket

inexpensive, high power, low energy

expensive, high power, average energy density, no

further improvement expected

Still expensive, lower power, high energy,

safety

World-wide

battery market From The Cobalt

report (2005)

Alternative LiB Materials Under Consideration: Voltage vs. CapacityCathodes

Anodes

LiCoO2

Li metal

“Issues and challenges facing rechargeable lithium batteries”, J.-M. Tarascon and M. Armand, Nature 414, 359-367 (2001)

C

Some Advances in the Anode Field: Nanoparticles and Composites

Metals and alloys show v. high capacities (e.g, Si = 4200 mAhg-1

approx. 10x that of graphite), but suffer from extremely large volume expansions

=> use a composite (of nanoparticles/domains) to absorb stresses during cycling (less problem with reactions with electrolytes at low voltage - fewer safety issues)

Field sparked off by the discovery of Tin-Based Amorphous Oxides (TCO): Sn1.0B0.56P0.4Al0.4O3.6 (Kubota, Matsufuji, Maekawa, Miyasaka, Science, 276, 1997)

TCO : SnO + SnO2 --> Li2O + Sn ----> LixSn

CoO + 2Li ---> Li2O + Co (740 mAhg-1)S. Grugeon… J.-M. Tarascon, 2003

Li2O

Other approaches - extrusion/displacement reactions

InSb + Li ---> Li3Sb + In --> LixIn Cu2Sb + Li ---> Li3Sb + In M. M. Thackeray, J. Vaughey (1999)

J. Dahn

Cu2.33V4O11 + x Li ---->

LixCu2.33-y V4O11 + yCu

M. Morcrette, J. -M. Tarascon (2001)

Reversibility?

What other cathode materials are being investigated?

Both Fe and Mn oxides have been studied extensively as alternative cathode materials (cheap and non-toxic)

E.g.: 3 dimensional structures such as:

-Manganese Spinels LiMn2O4 --> MnO2+ Li-Good electronic conductivity - high power

low capacity

LiFePO4 and related phosphates - low capacity-Poor electronic conductivity - good rate performance (with C coating)

New layered Materials such as Li(NiMn)0.5O2, Li(Co1/3Mn1/3Ni1/3)O2 (Mn4+)

High capacity --- poorer rate performance?

Layered lithium vanadates (for static power supplies)

LiFePO4

C

Improving the materials performance requires a fundamental understanding of how materials function and what structural/electronic properties limit battery

performance

Structures of the materials as they are cycledWhere are the Li+ intercalated into the structure?

Electronic properties - How do they change as Li+ is removed?

Ionic conductivitiesHow do the Li+ ions move through the lattice?

Effect of structure and electronic properties on voltage (e.g., Co3+ -> Co4+; Fe2+->Fe3+)

Li+ in oct vs. tet. sites

A whole variety of experimental and theoretical methods have been used to study these systems including: Electrochemistry (voltages … infer structural changes) Diffraction methods (long range structure) XANES (local structure and oxidation state) Solid state NMR (local structure)

•In theory, we can use NMR to study these systems and determine: where the Li+ ions are, their local coordination environments, and the Mn electronic structure

...…..at each stage of charge/dischargeto obtain fundamental information about how the battery works

Mn Oxidn states?

Mn(IV) (III)

WHY NMR?Solid State NMR can be used to obtain:

Local atomic structure + Local electronic structure

LiMn2O4

…and how the battery fails

We perform lithium NMR, since the lithium is directly involved in the electrochemical process...

But what is nuclear magnetic resonance (or NMR)?

Require nuclei (e.g., 1H, 13C, 6Li, 7Li,

31P) that have non-zero nuclear spins Spin-1/2 vs. quadrupolar (I>1/2) Nuclei behave like tiny bar magnets

in a magnet fieldBo

E

Each nucleus has a characteristic energy splitting E, which depends on the magnetic field strength B0 => element specific

Detect signal at frequency corresponding to E, with intensity proportional to no. of spins => quantitative

B0

NMR of Solids

Solid State 1H NMR Liquid NMR, e.g., CH3CH2OH

1H

HD = -D(3cos - 1)IzSz

D = I Sh/2r3

IrIS

S

•NMR spectra of solids are broadened by the anisotropic interactions (interactions whose magnitude depends on the orientation wrt field), e.g.,:

•Chemical shift anisotropy •Dipolar coupling (Nuclei interact with each other, in the same way that two bar magnets interact)•Quadrupolar interaction•6Li (I = 1); 7Li (I = 3/2)

•Much of the chemical information can be lost

•Cf liquids NMR where the tumbling of the molecules removes these interactions

Basement @ Stony Brook

Most of the anisotropic interactions may be removed by Magic Angle Spinning: The bigger the interaction,

the faster we need to spin

Bo

rt

= 5

4o 4

4’

(3cos2 - 1) = 0 Slow MAS

Faster MAS

Freq

uen

cy,

Rotor period = 1/r

time

Axial CSAPowder pattern

r

r

r

NMR is also very sensitive to motion

E.g., Two Site Exchangekr(A-B)

A <----------------> B

Fast exchange

k >> f

Slow exchange

k << f

Intermediateregime

k same order as f

f (Hz)

NMR can be used to:• extract correlation times and activation energies for motion•determine which sublattices are mobile

Timescale

Hz kHz MHz

Lineshape changes

T1

T2

T1

Loss of satellite

transitions

Many of the battery materials are paramagnetic, which introduces additional

complications

Mn4+ Co4+delectrons

Co3+

Li2MnO3 (LiMn2O4) LiCoO2 Li1-xCoO2B0

T1e

NMR timescale

eff

no field

Time averagedvalue of magnetic

moment

Magneticmoment-dependson the no.of unpaired e-

ESR NMR

In order to extract structural information, we need to understand the effect of the unpaired electrons on the NMR

spectra

The Fermi-contact shift results in large shifts - these shifts contain both structural and

electronic information

The Fermi Contact Shift: measure of the unpaired electron spin density transferred from the paramagnet to the NMR nucleus

Hc = IzAs<Sz> <Sz>

Mnt2g Li 5

20

1000 800 600 400 200 0

ppm

Fermi Contact Shift

Typical chemical shift for

diamagnetic compound

C.f. J-coupling and magnetic coupling

N

C

H

H

E.g., LiMn2O4 6Li MAS NMR

The dipolar interaction: through space coupling to nearby nuclear or e- spins

The sidebands are largely caused by the dipolar coupling, which contains geometric

information

B0

I rIS

<SZ>

Mn Li2MnO3

Li0.5Zn0.5[Mn1.5Li0.5]O4

Oh (4a)

Oh (2b)

Li

Mn

Zn

MnLi

•Very different sideband patterns are observed, depending on the arrangement of Mn around the central Li.

5000 4000 3000 2000 1000 0 -1000

** *********

** *

* * * * * * * * ********

755734

1461

684

2325

ppm

NMR spectra are also sensitive to electronic conductivity mechanism

Mn (16d Oh)

Li (8a Td)

52

01000 800 600 400 200 0

ppm

eg

t2g

• LiMn2O4 is a hopping semiconductor

• Li “sees” an average oxidation state=> only one local environment

C.f. metals - Knight shifts seen

But… how do we explain the different local environments seen in LiMn2O4 as a function of

synthesis temperature?

SynthesisTemperature

850 ºC

520

?

1000 800 600 400 200 0ppm

630

575

546

512

498

635 59

055

458

855

151

2

650 C

600 C

550 C

.. and obtain chemical information from these systems

Materials synthesized at lower temperatures show:•better cathode performance•higher average Mn (IV) oxidation states

Understanding the 6Li NMR Shifts: Use of Model Mn III/IV

compounds

l

l

l

l

l

l

l

l

l

l

l

MnO

Mn3O4

Li2Mn4O9

Li4Mn5O12

Li2MnO3

Li7Mn5O12

Li5Mn4O9

LiMnO2

LiMn3O4

λ-MnO2

-Mn2O3

(Mn4+)

(Mn4+)

(Mn4+)

(Mn3+)

(Mn4+)

LiMn2O4(Mn3.5+)

l

III

InsertionExtraction

Oct Li Tet Li

Mn3+ rock salts

2500 2000 1500 1000 500 0 -500 ppm

Mn4+ spinel

Mn3.5+ spinelTet Li

Mn4+ layered materialsLi in Mn4+ layers Li in Li layers

Mn3+, Mn4+

K2NiF4 cmpds

4000 2000 0 -2000

1980

847

687

ppm

Li2Mn4O9

Litet[Li1/3Mn5/3]octO4

Lithium “Hyperfine Shift Scale”

•use shift as a “fingerprint” of different Li local environments

The Fermi contact shift depends on the coordination environment & nature of the orbital

overlap

Compound Site No. of Li-O-MBonds

BondAngle

Mn oxidnState

NMR Shift

Li4Mn5O12 8a16d

(16c)

1212(6)

(12)

121.096.2±0.

3(171.9)(89.6)

4 8471980

Li2Mn4O9 8a 12 120.7 4 687Li2MnO3 4h

2b2c

48

1248

180909018090

4 905/850

1817/1770922/875

Mn

Li

O

16c

Li4Mn5O12

Li2Mn2O9

Li2MnO3

We can rationalize the shifts by using the same approach used to analyze magnetic couplings between

spins:

Transfer to an empty dz2: spins align

with e- in t2g orbitals to maximize exchange interaction

Bo

t2g

Li

t2g

dz2

+ve shift: ~ 300 ppm

-ve shift:

~ -100 ppm

90º

180º

Spinel:

122ºLi

12 x 122º12 x ~ 64 ppm

Mn

LiO

Mn

O

O

O

“Goodenough- Kanamori

Rules”

2 4 6 8 10

2

4

6

8

10

CoCr

90 deg interaction

Li180 deg interaction

LiCr1/8

Co7/8

O2

-275.0-200.0-125.0-50.00-20.00-10.00-5.00006.25025.00100.0175.0250.0325.0400.0475.0550.0

LiCoO2

90°interaction

Li

180°interaction

Cr O

Layered LiCr0.1Co1.9O2 +ve

0

-ve spin density= -ve shift

DFT calculations can be used to help understand the causes of these hyperfine shifts, by calculating

the unpaired e- spin density on Li

90°interaction

Plot spin densities of:Dany CarlierGerd CederMichel Menetrier

Co

Co

Co

Li

Li

Cr3+, d3; isoelectronic with Mn4+

I.e., unpaired e- densityt2g

EXAMPLE 1: The effect of cation doping on the Spinel Structure

E.g. I, Spinels: MnO2 (Mn4+) - + Li -> LiMn2O4 - + Li --> Li2Mn2O4 (Mn3+) One source of capacity fade comes from the Jahn Teller Distortion that occurs in the discharged state (for Mn oxidation states of 3.5 and less).

Expansion and contraction of the unit cell can cause grains to lose contact with each other and the carbon in cathode =>suggested to be responsible for severe drop in capacity

Potential solution: Cation doping is used to raise the average manganese oxidation state of Mn at the end of discharge to above 3.5

We can now use this hyperfine shift scale to investigate Li local structure in cathode

materials

Mn3+

Local Macroscopic

2500 2000 1500 1000 500 0 -500 -1000

* ***

67

4 63

95

83

55

0

23

00

ppm

Oct Li(spinel)

E.g., Li[Li0.05Mn1.95]O4 = Li[Li0.05Mn4+0.25Mn3.5

1.70]O4

5 “Mn3.5+” ions oxidized per Li+ dopant : Average oxidation state = Mn3.56+

Li - Excess Spinels

Mn3.5+

LiMn2O4

Tet Li

Increasing oxidation

state

1500 1000 500 0 -500 -1000

*** 67

4

63

95

83

55

0

y

x

Oct LiMn

(IV)

•Mn4+-rich regions are created near

Oct Li

Eg energy levels perturbed near the defect sites localization of e- holes

Mn4+ Mn4+Mn3+ Mn3+t2g

eg

DefectDefect

The Additional Resonances are due to Mn4+ sites near tet Li

Li Oct Site

Li(OMn3.5+)12-x(OMn4+)x

Lithium-excess materials are also formed at low temperatures, even for “stoichiometric”

compounds

520

850 C

1000 800 600 400 200 0ppm

630 57

554

651

249

8

635 59

055

458

855

1 650 C

600 C

550 C

7Li MAS NMR45 kHz MAS

4000 3000 2000 1000 0 PPM

2300

* **

**

513Oct. Li

Tet. Li

x406Li MAS NMR9 kHz MAS

LiMn2O4

Li1+xMn2-xO4

+ Mn2O3

Mn oxidnstate

increases

2500 2000 1500 1000 500 0 -500 -1000

**

**

**

* ***

* *

* *

* *

674639583

550504

2300

2300

718

649573

502

709

633562

499

746

501

ppm

LiCr0.1Mn1.9O4

LiNi0.1Mn1.9O4

LiZn0.1Mn1.9O4

Li1.05Mn1.95O4

Oh

Oh

283C

200015001000 500 0 -500-1000

* *

***

* *

*

* *

397

407

1390

1320

ppm

Oh

Td

Td•Helps explain why Zn2+ systems don’t work so well - Zn2+ in tet site

blocks Li+ diffusion (J. -S. Kim.. M. M. Thackeray, JES, ‘03)•Concentration of “extra” peaks related to oxidation state of dopant metal

Li NMR can be used to determine whether Li+ substitutes on the oct. or tet. site of the spinel

cathode materials LiM’xMn2-xO4

Following the Electrochemical Process

Swagelock-type Cell Li1.05Mn1.95O4 at 4V

End Bolt

Copper Plunger

Swagelock

Li AnodeFilter PaperPolypropyleneSeparatorLiMn2O4 Cathode

Battery Cycler

End Bolt

0 20 40 60 80 100 120 1403.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

Disharging

Charging

Potential (V)

Capacity (mAh/g)Capacity (mAhg-1)

Li1.05Mn1.95O4:

1st Charge

2500 2000 1500 1000 500 0 -500 -1000

635

556

627

797710

803708

2300

99 %

75 %

50 %

25 %

10 %

2100

0 %637

603

557525

616

618

592

534

485

488

ppm

Increasing Mn oxidation state

Li+ ions are removed from local environments containing progressively more Mn4+ ions as the charging proceeds

Li remains in the oct. site throughout

Li+- ion mobility increases - particularly in 1st 1/2 of charge

Oct Li

ppm

Loss of structure => Mobility

Fast exchangek >> f

Slow exchangek << f

Intermediateregime

k same order as f

f (Hz)

1000 500 0 -500

485

557

Li+ (+ e- ?) jump rates > 2 kHz

25%

10%

Lix [Li0.05Mn1.95]OhO4

Local Structure in Doped Spinels

Random cation (Li+) doping on the octahedral site will:

1. Create Mn4+ ions nearby the dopant cations

2. Prevent Li+ removal from sites near octahedral Li+

3. Create a 3D framework with a distribution of charges from 1 to 4+

All these factors help prevent the formation of a series of phases with long range lithium-ion ordering during cycling

=> Helps improve the capacity retention?

Oct. LiTet. LiPanasonic

Example II: Ni2+/Mn4+ Layered Cathodes, Li[NixMn(2-x)/3Li(1-2x)/3]O2: A Combined XAS, Diffraction,

DFT and NMR Study

These compounds may be viewed as solid solutions between Li2Mn4+O3 (Li(Li0.33Mn0.67)O2) and Li(NiMn4+)0.5O2

Li(Ni1/2Mn1/2)O2

DATA From: Z. Lu, D. D. MacNeil, J. R. Dahn, ESSL4, (2001) A191-A194.

V

LiNiO2

LiMnO2

Li[Li1/3Mn2/3]O2

x = 1/2 1/3 1/10 0

LiCoO2

Capacity: mAhg-1

Li(NiMn)0.5O2 (T. Ohzuku, J. Dahn)

Isostructural with LiCoO2

Oxidation/reduction process involves multiple electrons (Ni2+ -> Ni4+ ???)

Ni, Mn

Li

Approx. 200 mAhg-1 reversible capacity can be obtained

Similar capacities obtained by other groups for:

x = 1/2 (T. Ohzuka) Li excess materials (C. Johnson and M. M. Thackeray; Z. Lu and J. Dahn)

Is the redox active metal Ni2+? How do these systems function?

How does local structure effect electrochemical performance?

20 cycles C/20LiMn0.5Ni0.5O2

3000 2000 1000 0 -1000 PPM

Li in lithium layers

MAS speed: 36 kHz

•Li sites in Li and Mn layers readily resolved

*** * *

a. Local Structure:Li[Li1/3Mn2/3]O2

yz

Li 90Mn/CrMn

Mn

c

c

c

4000 2000 0 -2000

ppm

yz

Li 90Mn/CrMn/Ni

Li in the Ni/Mnlayers near

Mn4+

Li2MnO3

shifts

Ni doped compounds show similar spectra

•Li2MnO3-type local environments still observed

Mn:6 5

yxz

90

LiLi

Mn/Cr

Mn/Cr

180

Mn/Ni

Li in the Li layers

Li[Li1/9Mn5/9Ni3/9]O2

Ni2+ (d8) no unpaired t2g e-

4000 2000 0 -2000

ppm

“Li[Ni0.5Mn0.5]O2”

•6Li NMR shows that there are still Li ions in the Ni/Mn layers, near Mn4+ even tho’ these are not predicted based on the stoichiometry

yz

Li 90Mn/CrMn/Ni

Li in the Ni/Mnlayers near

Mn4+

Li2MnO3

shifts

•This is consistent with Ni2+ substitution in the Li layers (c.f. Dahn 2002)

ppm

Li+[Ni2+0.5Mn4+

0.5]O2 -->

Li1-xNix[Mn0.5Ni0.5-xLix]O2

Ni/Mn

Li

Neutron Diffraction (ISIS, GEM) are consistent with Ni2+/Li+ exchange model

10-2

110

101

006104

009

10-8

Bank 4

Rwp = 6.32%

7Li(Ni0.5Mn0.5)O2 Extra peaks:

superstructure peaks as seen for honey-comb ordering of Li2MnO3 (J. Solid-State Chem. August 2005)

Exchange of Ni and Li ions between the TM and Li layers: 8 ± 2 % of site exchange: consistent with NMR

Mn

Li

Li/Mn layer in Li2MnO3

4000 3000 2000 1000 0 -1000 -2000 -3000

567

776

1365

1560

x = 1/10

x = 1/3

x = 1/2

ppm

Li in the Ni/Mnlayers near Mn4+

Li2MnO3

shifts

Local structure as a function of Ni content?

Li in the Li layers

•Li in Ni/Mn layers is predominantly near Mn4+ and not Ni2+

for all compositions

•What does this tell us about the cation ordering in the Ni/Mn layers?

Li[Ni1/10Mn19/30Li8/30]O2

LiNi0.5Mn0.5O2

Li[Ni1/3Mn5/9Li1/9]O2

yz

Li 90Mn/CrMn/Ni

A Model for Cation Ordering in the Ni/Mn layers

Ni content Local environment ProbabilityExpt.

(I) Random (II) Ni for Li

x = 1/10 Li(OMn)6 0.06 .74 .73

Li(OMn)5(ONi) 0.06 .23 .27

Li(OMn)5(OLi) 0.16 .0

Li(OMn)4(ONi)2 0.02 .03negligible

Li(OMn)4(ONi)(OLi) 0.13 .0

Li(OMn)4(OLi)2 0.17 .0

Mn

a

c

c

c

c

Average charge of cation in layer = 3+ (c.f. LiCoO2)

Li2MnO3: Li+ : 2Mn4+ Honeycomb ordering minimizes Li - Li contacts

How can we minimize Ni2+ - Li+ contacts?

A Model for Cation Ordering in the Ni/Mn layers

Ni content Local environment ProbabilityExpt.

(I) Random (II) Ni for Li

x = 1/10 Li(OMn)6 0.06 .74 .73

Li(OMn)5(ONi) 0.06 .23 .27

Li(OMn)5(OLi) 0.16 .0

Li(OMn)4(ONi)2 0.02 .03negligible

Li(OMn)4(ONi)(OLi) 0.13 .0

Li(OMn)4(OLi)2 0.17 .0

Mn

Replace on 1 Mn4+

and 2 Li+ sites by 3 Ni2+

Ni

a

c

c

c

c

A Model for Cation Ordering:High Ni content

Ni content Local environment ProbabilityExpt.

Model II. Ni for Li

X = 1/3 Li(OMn)6 .34 - .6 .55

Li(OMn)5(ONi) .6 - .4 .45

Li(OMn)4(ONi)2 .05 - .0negligible

Mn Ni

Li

III Li/Ni avoidance

Maximize

Li-Ni avoidanc

e*

A Model for Cation Ordering:High Ni content: Ni = 1/2; 9 % Li in Ni/Mn

Layer

Ni content Local environment Probability Expt.Model II. Ni

for LiX = 1/2 Li(OMn)6 .18

.35Li(OMn)5(ONi) .36 .65

Li(OMn)4(ONi)2 .30 negligible

Li(OMn)3(ONi)3 0.13 0

III Li/Ni avoidance

Ni Ni

Li

C.f. Lu, Chen and Dahn, Chem Mat ‘03

?Ni/Mnordering

Using the total scattering to obtain local ordering: Pair Distribution Analysis (PDF) of neutron diffraction data

•Uses total scattering: Bragg and Diffuse•Provides local structure

Rwp = 6.32%

Li(Ni0.5Mn0.5)O2

to give g(r) - radial distribution function

-40

-30

-20

-10

0

10

20

30

40

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

7Li(NiMn)0.5O2

7LizeroNi0.5Mn0.5O2

6Li(NiMn)0.5O2

7Li7Li ZERONi6Li

Coherent scattering lengths (fm):

Ni: 10.30; 62Ni: -8.70 7Li: -2.22; 6Li: 2.00

Mn: -3.75

r (Å)

Ni,Li-O: 2.07 Å

Mn-O: 1.95 Å

M-M

7Li-O

6Li-O

04)(

12

δ rrrb

bbr i j

ijji −

⎥⎥⎦

⎤

⎢⎢⎣

⎡−∑∑gC(r) =

Use of different isotopes allows different M-M and M-O contacts to be separated

Fourier Transform

REVERSE MONTE CARLO SIMULATIONS:

•Generate giant cell•Randomly swap atoms in ab planes •If swap improves fit of PDF, swap is allowed

RMC

Random

After RMC

R-3m space group 12*12*2 cluster

Before RMC After RMC

%Ni-Ni pairs 16.1% (418 pairs) 11.8% (306 pairs)

%Ni-Mn pairs 42.4% (1099 pairs) 50.2% (1301 pairs)

%Mn-Mn pairs 24.2% (626 pairs) 20.7% (536 pairs)

%Li-Mn pairs 9.1% (235 pairs) 8.8% (227 pairs)

%Li-Ni pairs 7.8% (201 pairs) 8.1% (209 pairs)

%Li-Li pairs 0.50% (13 pairs) 0.5% (13 pairs)

Total 100% (2592 pairs) 100% (2592 pairs)

CorrelationcNiMn*

-0.04 -0.23 (± 0.04)

Correlation cLiNi* -0.09 -0.16 (± 0.1)

CorrelationcLiMn*

-0.06 -0.06 (± 0.1)

Ni/Mn Ordering ?

Li

Mn

Ni

Mn ring

Ni ring

Flower: A. van der Ven, G. Ceder, Electrochem.

Commun. 2004

Ni

Honey combNMR; Yoon et al.TEM; Meng et alESSL 2003/2004

1st coordination shell (%) 2nd coordination shell (%)

Orderingschemes

10*10*2 Orderingschemes

10*10*2

Order-ed

flower

Order-ed

Honey-comb

Rand-om

AfterRMC

Order-ed

flower

Ordered

Honey-comb

Rand-om

After

RMC

Ni-Ni

pairs

16.67 13.75 16.4 12.0 16.67 20.50 16.9 21.1

Ni-Mn

pairs

50.00 47.50 42.0 50.5 33.33 25.00 41.1 33.5

Mn-Mnpairs

16.67 18.75 23.2 19.1 33.33 37.50 23.7 27.2

Test the PDF Data Against Different Structural Models

Flower: Carlier, A. van der Ven and Ceder

Can we combine all the experimental data to provide more constraints all the

on ordering?

EXAFS - Mn near 1-2 Li and 4-5 Mn/Ni (Yoon et al.)PDF - Ni near < 3 Ni; Ni near 3 Mn

Simple honey comb impliesA. Too few Li(OMn6) sitesB. Too many Li(OMn4)(ONi)2 sites

NMR

III Li/Ni avoidanceIV Constrain Ni-Ni contacts

Ni Ni

Li

Disordered flower motifs emerge..

•Large coulombic energy associated with Li+ /Mn4+ “honey-comb ordering” drives Li

substitution in Ni/Mn layer and Ni substitution in Li layer

•difficult to make a pure layered material directly

How does Li ordering and Li/Ni exchange affect electrochemical performance?

1

2

3

4

5

Pot

entia

l / V

vs.

Li/L

i+

0 100 200 300 400

Capacity / mAhg-1

Voltage Profile for LiNi0.5Mn0.5O2

Battery cycler

b. Electrochemistry: The Redox-active metal?

8.33 8.34 8.35 8.36

0.0

0.3

0.6

0.9

1.2

1.5

1.8

(b)

Normalized Intensity (a. u.)

Energy / KeV

pristine scan 3 scan 6 scan 9 scan 12 scan 14 LiNiO

2

In situ XAS experiments show that the Ni is oxidized on charging

Ni

K-edge

LiNiO2

Charging

6.535 6.540 6.545 6.550 6.555 6.560 6.565 6.570

0.0

0.6

1.2

(a)

Normalized Intensity (a. u.)

Energy / KeV

pristine scan 3 scan 6 scan 9 scan 12 Li

2MnO

3

Mn

K-edgeLi2MnO3

With X. Yang, and J. McBreen, BNL

yxz

90

LiLi

Mn/Cr

Mn/Cr

180

4000 2000 0 -2000 -4000

594

13701486

711

X = 0.6

X = 0.3

X = 0.1

X = 0.0

ppm

Mn/Ni

layer

•Li NMR results show that Li is removed from the Li layers and the Ni/Mn layers

Li Layer

Li0.4Ni05Mn05O2

Mn/Ni/Li

Mn/Ni

LiNi0.5Mn0.5O2

Li0.9Ni05Mn05O2

Li0.7Ni05Mn05O2

Which Li sites are involved in the electrochemical processes?

CHARGE

Sites in the transition metal layers are always thought to remain stuck in the layers

4000 3000 2000 1000 0 -1000 -2000 -3000

L[Ni1/3

Li1/9

Mn5/9

]O2 powder

after first cycle between 4.8 and 2.5 V

ppm

End of 1st cycle, discharge to 2.5 v

Li in Ni/Mn layers

4000 2000 0 -2000 -4000

590

13241498

733

231 mAh/g

154 mAh/g

77 mAh/g

24 mAh/g

pristine

ppm

Pristine vs. end of 1st charge cycle

x=1

x=0.9

x=0.7

x=0.4

x=0.1

CHARGE

NMR of Li[Li1/9Ni1/3Mn5/9]O2 shows that the Li in the T.M. layers is removed on charging, but it returns

on discharging

Li is not inert

Oxygen

Li Layer

Metal Layer

Li in metal Layer

Calculations* were used to understand the mechanism for Li extraction out of the

Ni/Mn layers

How and why does this happen?

*J. Reed, A. van der Ven and Gerd Ceder

Spontaneous migration into Li layer

Oxygen

Li Layer

Metal Layer

2000 1000 0 -1000

after 20 cycles

ppm

Mn/Ni

layer

Li Layer

**

Extended Cycling or Cycling to High Voltage: Li does not return to the transition metal layer

pristine

To 4.6VTo 5.3 V

pristine

5.3V4.6V Ni, Mn, Li

Li, Ni

Ni, Mn

Li

Charge to high V

What exactly is going on?

Conclusions

NMR spectra are very sensitive to local structure and electronic structure.

•The spectra can be rationalized by considering the overlap between the Li, O and Mn (paramagnet) orbitals

•This has been used to spinels to:

•Locate Li on oct vs. tet sites

•Examine effect of doping on electronic structure

•Follow the electrochemical process

• and in Li[NixLi1/3-2x/3Mn2/3-x/3]O2 to:

•Determine occupancies for Li in the transition metal layers

•Derive a model for cation ordering in the transition metal layers

•Follow the changes that occur on cycling the battery

•(The Lis in the T.M. layers can participate in the electrochemical process; --> mechanism for increasing cation disorder following multiple charge cycles)

Ni

NexelionSONY’s new LiIB:

LiCoO2 + CoNiMn layered oxide

hybrid cathode+ C/Sn hybrid

anode

33% more capacity

Part II:

NMR Studies of Oxygen Ion Motion

Why is Anionic Mobility Important?

The SOFC O2/H2 Cell

Porous anode Doped ZrO2 Porous

Electrolyte Cathode -for stationary power

O2 + 2e- -> 2O2-

H2 ->2H++2e-

H2

*Requires high temperatures (1000 oC for thick electrolytes)

O2-

H2O e- O2 (air) Fuel FlowAir Flow

Fuel electrode

electrolyte

Air electrode

Porous Support Tube

Interconnection

Other applications that require anionic conduction include..

O2 Sensors

• Lambda O2 sensor for O2

detection in cars

• (regulate gas/O2 ratios)

• -again uses YSZ

• -high temp (500 ºC) required for rapid response

O2/N2 Separations

Problems with SOFCs

High operating temperatures Expensive - particularly due to materials

required for high temp. operation (Ceramic vs. stainless)

Stability of materials at high temperatures Degradation of seals

Solutions ----> Improve catalyst in electrodes (particularly on cathode side)

Improve ionic conductivity of electrolyte

Increase surface area of 3-phase boundary

Use thinner electrolytes

LSM

Electrolyte (YSZ)

O2 O2

O2-

O2- O2-

<- e-

cathode

O2

Improving Ionic Conductivity Investigate known alternative electrolytesLSGM - alternative to YSZ for “low temperature” (700 ºC) operations

Improve our understanding of mechanisms for ionic conduction - better electrolytes?

O=X

Ga (Mg)

=B

La (Sr) =A

Sr2+ and Mg2+ doped LaGaO3

YSZ

J. Goodenough

How Do Oxygen Anions Move in Solids?

Vacancy mechanism Interstitial Mechanism

Vacancies/interstitials are created in a solid by cation doping: e.g. Y3+ - doped ZrO2 YxZr1-xO2-x/2 x/2

c.f., Y3+ - doped CaF2 YxCa1-xF2+x interstitial F-

Major mech. for

O2-

So what’s the problem?

Large activation barriers, due to the 2- charge on the anion => need high T.

Since the vacancy is produced by adding a lower valent cation….

…vacancy-dopant clustering can occur at low temperatures

3+

4+

2-

3+

4+

2-

e.g., Y3+-ZrO2

Many anionic conductors show considerable disorder on the anion sub-lattice. - diffraction studies do not necessarily provide an accurate model for the local structure.

However… the nature of the defects and local order controls the mechanisms of conduction in these materials.

If we can observe the different oxygen sites in the structure by NMR, then we can determine which oxygen anions are responsible for the anionic conductivity.

3+

4+

2-

Understanding the conduction process: Why NMR?

The BIMEVOX Family (Bi4V2-xMxO10-x/2) - some of the highest oxide conductors discovered to

date

-Bi4V1.7Ti0.3O10.85

Bi4V2O11

Conductivity of selected oxide materials, after Kendell et al. Chem Mat, ‘96, and Yan and Greenblatt, SSI ‘95.

Max. temp.

reached by

standard commercial probes

The 17O chemical shift is very sensitive to the local environment, so it should be possible to determine mobilities for different sites…. e.g., Y2(SnyTi1-y)2O7

Y2Ti2O7

Y2Sn2O7

Y2(Sn0.4Ti0.6)2O7

Y2Sn2O7

OSn2Y2

OY4

OTi2Y2

OSnTiY2

•Determine the Sn/Ti ratio

17O I = 5/2

17O I = 5/2

x yz

Two Site Exchangekr(1-2)

F(1 )---------------->F(2)

<--------------

kr(2-1)

c =

2x10-5s

2x10-4s

2x10-3s

NMR Studies of Motion: Well established for systems where motion approaches the NMR

(chemical shift) timescale near R.T.: E.g., fluorides

Temp.(ºC)R.t.

120

160

200

250

-PbF2

Alpha-PbF2

1000 500 0 -500 PPM

The conductivity may be dramatically enhanced by substituting the M6+ cations by M5+ cations, either

stoichiometrically or by doping

e.g., Bi4V2O11

= Bi2VO5.5 �0.5

Nb5+-doped Bi2WO6

830

615

Bi2O22+ layers

c.f., Bi217O3

δ = 195 ppm

(S. Yang et al. JACS 1989)

17O MAS NMR 8.4 T VO5 �0.5

“octaheda”

= 10 -5 vs. 10-3 Scm-1

at 500 °C (Nb)

Baux et al. SSI 1996

WO6

With R. -N. VannierLille

1000 800 600 400 200 0 -200 PPM

Bi2WO6

Bi2W0.9Nb0.1O5.95

•Heat in 17O2 gas at 600 °C

17O enrichment is straightforward for moderate conductors

X 5

= 10 -5 vs. 10-3 Scm-1 at 500 °C

(Nb) Baux et al. SSI 1996

Bi2O22+

layers17O MAS NMR

8.4 T

WO6

RT

150oC

225oC

250oC

200oC

Since we can resolve the different sites by NMR we can then determine by NMR which oxide ions

are responsible for conductivity

500 400 300 200 PPM

Coalescence => c= 7000 s-

1

•Motion occurs via anion vacancy jumps between the axial and equatorial WO6 oxygen atoms

•Oxide ions in the Bi2O2

2+ layers are rigid

Bi2O22+ layers

Two site exchange

500 400 PPM

5% Nb5+

500 400 PPM

10% Nb5+

RT

100oC

150oC

250oC

200oC

T

Increasing the doping level increases the mobility, consistent with an anion vacancy

model

in contrast to earlier literature reports..

2x4s 3 x5s

o Bi2WO6

Bi2W0.95Nb0.05O6

Bi� 2W0.9Nb0.1O6

The NMR results are consistent with newconductivity data (on the same samples)

NMR measurements

Probing much slower motion:2-Dimensional NMR methods

/2 /2

Preparation

Mixing

t1

π/2t2

Detection

Evolution

F1

F2

A

B

A-B

B-A

AB• Probe motion that occurs during the “mixing time”

Room temperature tm=50ms

175oC tm=5ms

250oC tm=5ms

225oC, tm=5ms

c for W-O ax and eq exchange ~ 10 s, while c for

W-O/ Bi-O exchange ~ 10

ms

Bi2O2 layer

W-O-W

W-O-Bi

2-D NMR methods can be used to detect the slower jumps between the Bi2O2

2+ and WO6 layers

Variable Temperature 17O MAS NMR spectra of Bi4V2O11can again be used to determine directly

which sites are mobile

17O MAS NMR

2000 1000 0 -1000 PPM

30oC

100oC

140oC

180oC

220oC

250oC700

260

830615

* *

•The resonances at 615ppm and 830ppm gradually merge oxygen motion in the vanadium oxide layer increases as the temperature increased

•Both V-O oxygen sites are involved in the motion.

900 700 PPM

900 700 PPM

*

*

600 MHz data

V-O-VV-O-Bi

Now 51V MAS NMR may be used as a 2nd probe of structure (& motion) in this more complex material

Idealized Structure of the high temperature phase

Structure refinements*:

2 tet, 2 penta coord V sites 3 tet, 1 penta coord V sites

*R.N. Vannier, G. Mairesse et al.0 -200 -400 -600 -800 PPM

-430 tetsym.

-510tet V:II(distorted)

-4405-coord

51V MAS NMR

40 kHz

15 kHz

1:1

**

*

* *

Abrahams, I. J. Mat. Chem. 1998. Hardcastle, F. D. JSSC 1991. Delmaire, F. PCCP 2000

17O/51V TRAPDOR NMR of Bi4V2O11confirms that the resonances at 610 and 820 ppm are near vanadium.

Use to detect motion between the same sites

17O/51V TRAPDOR at 10kHz spinning

No irradiation

51V irradiation for 800msec(rf = 100 kHz)

Difference

2000 1000 0 -1000 PPM

610

265

820

= nR

90o 180o

17O

51V

•The TRAPDOR effect decrease substantially at 180 ºC as these sites become mobile

c ~1 ms

17O

51V

Motion is seen at room temperature for the fastest anionic conductor Bi4V1.7Ti0.3O10.85!

17O; 18 kHz Oxygen in the Bi-O layer

V-O layer

30oC

100oC

180oC

250oC

670

260

677252

1000 0 PPM

-100oC

-140oC

0oC

1000 0 PPM

17O; 9 kHz

•No TRAPDOR effect until -100 oC

80 70 60 50 40 30 20PPM

Rt

100C

150C

200C

250C

250 200 150 100

200C

RT

LaGaO3: 71Ga and 17O Can be Used to Probe Local Structure

71Ga NMR

Pnma

R3c

17O NMR: No evidence for O mobility

17O (and 71Ga) are quadrupolar nuclei; Large QCCs imply anisotropic

environments for O

mI

-5/2

-3/2

-1/2

+1/2

+3/2

+5/2

0

Central Transition

0-Q’

0-2Q’

0+2Q’

0

0+Q’

0

0

0

0

Central Transition

Central Transition

HQ(2)HQ

(1)HZ

2nd order quadrupolarlineshape - extract QCC(3.1 MHzeta close to 0)

Vzz

Cation Doping Increases O Mobility, as Seen by 17O NMR

350 300 250 200 150 100 50 PPM

250C

200C

150C

100C

Ambient

300 250

200 150

rt

250C

10% Sr 10%Mg2+

Mg-O-Ga

Collapse of 2nd order lineshape=> hops between sites

Vzz

Summary

•Local probes such as NMR and PDF analysis can be used to examine both local and long-range motion in perovskite-like materials

•We have now developed a number of approaches that allow us to follow oxide ion mobility in solids at moderate temperatures1. Normal VT methods (for more mobile systems), for hops between different sites2. Two dimensional NMR experiments allow us to study much slower motions

(up to correlation times of approx 100 ms)

•These methods yield detailed information concerning which and how oxide anions move in solids

This approach has been used, e.g, in Nb5+-doped Bi2WO6 to show that:•motion involves jumps between the two sites in the WO6

2- layers

•Motion in 3D occurs with a much longer correlation time

•Methods are being applied to materials with lower conductivity such as doped LaGaO3

Acknowledgements

Wonsub Yoon (BNL)

Younkee Paik

Nicolas Dupre (CNRS, Nantes)

Stony BrookYoung Joo Lee (LG

Chemicals)Namjum Kim

(Stanford)

CEMS

BNLXing Yang

James McBreenLille

Rose-Noelle Vannier

John PalumboJulien Breger

Meng Jiang

NSF, DOE (Office of FreedomCAR) and Gillette

MIT Gerd Ceder

Dany Carlier (Bordeaux); Anton van der Ven (U. Michigan); John Gorman; John

Reed; Shirley Meng; Kisuk Kang

Yang Shao-Horn