Studies of Li-ion Battery Materials using XAFS Spectroscopy

Mali BalasubramanianSector 20, Advanced Photon Source

Argonne National Laboratory

2

Acknowledgments

Research supported by the U.S. DOE

N. Karan and S.Pol (Sector 20)

J. McBreen, W. S. Yoon, X.Q. Yang and X. Sun (BNL)

D. Abraham, S-H. Kang, J. Bareno, L. Trahey, C. Johnson, I. Belharouak, M. Thackeray and K. Amine (ANL)

G. Jain (Medtronic Inc.), J.J Xu ( Rutgers Univ.), A. Mansour (NSWC)

S. Heald, R. Gordon, D. Brewe ( Sector 20)

D. Fischer (NIST), K. Pandya (X-11A, NSLS),S. Khalid (X-18 B)

I. Davidson (NRC, Canada).

3

How Does the Battery Store and Generate Electricity

During discharge each electrode undergoes a half cell reaction

At the anode the reaction is:

LiC6 6C + Li+ + e-

At the cathode it is:

Li0.5Co(III)0.5Co(IV)0.5O2 + 0.5Li+ + 0.5e LiCo(III)O2

The driving force for the external current is the difference in electrode potentials of the half cell reactions. This yields an operating voltage of 3.7 V

4

Approach

X-ray Absorption Fine Structure Element specific, sensitive to dilute constituents ( sub-mono layer coverage), short-range order probe

Resonant and Non-resonant X-ray EmissionDirect sensitivity to spin state of the transition metal ions, allows for partial fluorescence yield measurements

Hard X-ray Non-resonant RamanCombines the in situ capability of hard x-rays with the power of soft x-rays, q-dependence provides additional information

Combine above techniques with grazing incidence/total reflection geometries to obtain surface/interface sensitivity

5

Crystal Structure of Layered LiCoO2 and LiNiO2OctahedralLi: (0,0,0)Ni,Co: (0,0,1/2)Tetrahedral(0,0,z) with z ~0.125 and 0.375

Li

NiO2

LiNiO2 tends to be non-stoichiometricwith excess Ni occupying Li sites

Li2MnO3: Li (Li1/3Mn2/3)O2 in layered notationTM layers: Li+ and Mn 4+ ; √3x√3 charge ordering

6

MnO2 Polymorphs

•Various polymorphs: reveals the versatility of MnO2

•Used in both primary and secondary batteries

•Appealing redox behavior make them prime candidates for Li-air electrocatalyst applications

7

IN SITU XAS OF PROMISING CATHODE CHEMISTRIES

LiNi0.85Co0.15O2

NCA: LiNi0.8Co0.15Al0.05O2

Nano-Fe2O3Nano-FeOOHLFP: LiFePO4

LiMn2O4LiNi0.5Mn0.5O2

NCM: LiNi1/3Co1/3Mn1/3O2LiNi1-xCr2xMn1-xO2Li[Li0.2Co0.4Mn0.4]O2Li[Li 0.2Mn 0.4Cr0.4]O2Li[Li 0.2Mn 0.4Fe0.4]O2

Nano-Li2MnO3

Chevy Volt PHEVFord Escape PHEV

8

X-rays

Energy (eV)7400 7600 7800 8000 8200 8400 8600 8800

Abs

orpt

ion

1

2

3

Energy (eV)7700 7710 7720 7730 7740 7750

Nor

mal

ized

XA

NE

S

0.0

0.5

1.0

1.5

XANES

EXAFS

X-RAY ABSORPTION SPECTRUM FOR LiCoO2 AT Co K EDGE

Interference of outgoing and backscattered photoelectron wave at the vicinity of the central atom produces EXAFS

• In situ measurements

• Chemical and structural information

• Short range order probe (local and medium range)

• Element specific technique

• Complementary to average structure methods

Why XAS for batteries ?XANES

0 2 4 6 8 10 12k²χ(

k)

k (Åˉ¹)EXAFS

X-ray Absorption Spectroscopy

9

XANES GIVES INFORMATION ON OXIDATION STATE AND COORDINATION SYMMETRY

Mn

O O

O O

O

O

Mn

O

O OO

Octahedral

Tetrahedral

Mn

MnOMn2O3

MnO2

KMnO4

1s 3d

1s 4p

10

Structural Information in the Local Scale: EXAFS

0 2 4 60

2

4

6

8

10

12

14

16

C

B

A

Four

ier T

rans

form

Mag

nitu

de (A

.U.)

R (Angs.)

MnO2 - Pyrolusite As-prepared MnOx

EXAFS FT of MnO2 pyrolusite standard compared with amorphous MnOx.

Polyhedral approach

Edge and corner sharing

Edge sharing

Relative ratio of edge/face-corner sharing changes with structure in many oxides : Topological approach

Manceau et al. ( late 80’s-90’s)

First shell (Mn-O) parameters:N = 5.9±0.79 σ2=0.0036±0.0012 Å2

RMn-O = 1.897 Å ± 0.009

Edge sharing Mn-Mn :N = 5.7±2.9σ2=0.0065 ± 0.0045 Å2

RMn-Mn= 2.869 Å ± 0.030

Corner sharing Mn-Mn :N = 1.6±2.4σ2 = negative valueRMn-Mn= 3.421 Å ± 0.030

Acid treated (AT) Li2MnO3: electrocatalyst for Li-air

Note large error bars in N and disorder, primarily from correlations. Also, unphysical negative disorder for CS Mn-Mn correlation

Mn-O

ES

CS

Li-air studies by Naba Karan

12

The previous fit failed, why?

data range 3-11 k; fit range 1.0-3.45 Å12 independent parameters but 11 parameters varied

N,R, σ2 for each path Mn-O, ES Mn-Mn and CS-Mn-Mn, 2 enot’s for Mn-O and Mn-Mn

Information content is equally spread in r-space Mn-Mn correlations contribute in the 2-3.45 Å range; this corresponds to maximum of ~ 2*8*1.4/3.14 ~7 independent data points

7 parameters related to Mn-Mn correlations variedNote: Independent data points from the 1-2 Å range do not contribute to information content in the Mn-Mn correlation r-range

In this case we need to constrain disorder to reasonable values, if coordination numbers have to extracted

13

Fit of MnO2: Pyrolusite standard k: 3-14.5 Å-1

R fit range: 1.1-3.45 Å

Used to obtain S02 ,

0.71(5), and values for disorder for the Mn-Mnedge shared and corner shared contributions

Coordination numbers fixed at crystallographic values

Mn-O

ES

CS

Structural parameters similar for smaller k-range: 3-11.5 Å-1

14

Li-air electrocatalyst : “constraint” disorder of Mn-Mn ES and Mn-Mn CS using values from Li2MnO3 and MnO2 standard

Set ss_ES = 0.0028 Å2

ss_CS = 0.0037 Å2

Mn-O

ES

CS

First shell (Mn-O) parameters:N = 6.1±0.70σ2=0.0035±0.0014 Å2

RMn-O = 1.904 Å ± 0.009

Edge sharing Mn-Mn :N = 3.6±0.3RMn-Mn= 2.85Å ± 0.01

Corner sharing Mn-Mn :N = 3.2±0.7RMn-Mn= 3.42 Å ± 0.02

Physically plausible numbers and reasonable error bars.

15

Time [mins]0 60 120 180 240 300 360 420 480 540 600

Volta

ge [V

]

3.25

3.50

3.75

4.00

4.25

4.50

4.75

5.00

5.25

5.50

1

23

45

67

89

1011

1213

1415

1617

1819

20C/10 charging rate

Fresh Li1-xN i0.85Co0.15O2 cathode material

XAFS scans can be performed in a couple of minutes; so cycling can be performed at faster C-rates, if required.

Ni FT k-range: 3.0-15.0 Å-1

R [Å]0 1 2 3 4 5 6

k3 tra

nsfo

rm m

agni

tude

0

5

10

15

20

25

30

X=0X=0.3X=0.6X=1.0

Co FT k-range: 3.00-11.5 Å-1

R [Å]0 1 2 3 4 5 6

k3 tran

sfro

m m

agni

tude

0

5

10

15

20

25

X=0X=0.3X=0.6X=1.0

Co and Ni Fourier transforms for Li1-xNi0. 85Co0.15O2

Co-O Ni-O

Ni-TMCo-TM

Co3+ Jahn-Teller inactive Ni3+ Jahn-Teller active

R [Å]0.5 1.0 1.5 2.0 2.5 3.0 3.5

Im {F

(r)}

-40

-20

0

20

40

60

X=0

X=1.0

Black: DataRed: Fit

Fit to Ni XAFS of Li1-xNi0.85Co0.15O2

Imaginary part of FT is displayed; arrows indicate fitting range covered

Analysis performed using FEFF 6 and Newville-Ravel XAFS analysis software

0.0 0.5 1.0Bo

nd d

istan

ce [Å

]

1.90

1.95

2.00

2.05

2.10

0.0 0.5 1.0

Coor

dina

tion

num

ber

0

1

2

3

4

5

6

7

Long Bond

Short Bond

Long Bond

Short Bond

Value of x in Li1-x(Ni/Co)O2 Value of x in Li1-x(Ni/Co)O2

Bond distance and coordination number for the first Ni-O shell

Pure LiNiO2: Ni(III)-O = 2 @ 2.05 Å and 4 @ 1.91 Å; Ni-Ni = 2.87 ÅIn Ni standards: Ni(II)-O = 2.05 Å and Ni(IV)-O = 1.88 Å

Co-O vs Weighted Average Ni-O

0.0 0.5 1.01.86

1.88

1.90

1.92

1.94

1.96

Ni-Ni and Co-Ni bond distances

0.0 0.5 1.02.80

2.81

2.82

2.83

2.84

2.85

2.86

2.87

2.88

Col 23 vs Col 24 Col 23 vs Col 26

NiCo

Bon

d di

stan

ce [Å

]

Bon

d di

stan

ce [Å

]Value of x in Lix(Ni/Co)O2 Value of x in Lix(Ni/Co)O2

Co-O vs Weighted Average Ni-O

0.0 0.5 1.01.86

1.88

1.90

1.92

1.94

1.96

Ni-Ni and Co-Ni bond distances

0.0 0.5 1.02.80

2.81

2.82

2.83

2.84

2.85

2.86

2.87

2.88

NiCo

NiCo

Bon

d di

stan

ce [Å

]

Bon

d di

stan

ce [Å

]Value of x in Li1-x(Ni/Co)O2 Value of x in Li1-x(Ni/Co)O2

XAFS determined bond distances for Li1-xNi0.85Co0.15O2

Pure LiCoO2: Co (III)-O = 1.91 Å; Co-Co = 2.82 ÅPure LiNiO2: Ni(III)-O = 2 @ 2.05 Å and 4 @ 1.91 Å; Ni-Ni = 2.87 ÅIn Ni standards: Ni(II)-O = 2.05 Å and Ni(IV)-O = 1.88 Å

Summary : Li1-xNi0.85Co0.15O2

• Delithiation of Li1-xCo0.15Ni 0.85O2 leads to the oxidation of Ni3+ to Ni4+ . The presence of non-cooperative JT around Ni3+ is evident. Local structure and structural evolution around Co and Ni are distinctly different.

• To within the accuracy of the XAFS technique, Co occupies Ni-type sites (in the NiO2 slabs).

• Co doping has a strong effect on the overall structural evolution and leads to the expansion of the a and b axes close to the end of charge.

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Mn-Based Systems• Spinel: LiMn2O4 Charge (4V plateau) λ−ΜnO2

Mn (3.5)Mn (4) (Li removed from tetrahedral sites)• LiMn2O4 Discharge (3V plateau) Li2Mn2O4

Mn (3.5) Mn (3) (Li inserted from octahedral sites)

Only 50% capacity can be utilizedMn (III) exhibits large cooperative Jahn-TellerCurrently considerable interest in developing layered Mn-oxide materials (unique Li site and also reduce Jahn-Teller effect)

Layered LiMnO2: unstable on cycling; reverts to spinel on cyclingLayered (R-3m) Mn-Cr based oxide: Li[LixCryMn1-x-y]O2

Li2Mn4+O3 LiTM3+O2(M3+=Co3+, Ni3+,Cr3+)

TMO6octahedra

•= Li•= Li•= Li•= Li+

Integrate layered-layered system

Obtain structural stability from Li2MnO3[Li(Li0.33Mn0.67)O2]

Li+ and Mn4+ charge ordered in TM plane

Perform electrochemistry with LiTMO2

22

LiCrO2:Li2MnO3 LiNiO2: Li2MnO3

Lu and Dahn: JES, 149 A1454 (2002); Electrochem. Solid State Lett. 4 A191 (2001).

23

Local Structure: Li(Li0.2Co0.4Mn0.4)O2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1 3 5 7 9 11

k (Åˉ¹)

k²χ(k)

Li2MnO3Mn:Co

Mn-edge

-3

-2

-1

0

1

2

3

1 3 5 7 9 11

k (Åˉ¹)

k²χ(k)

Co-edge

Mn:Co

LiCoO2Mn:Co

•Mn XAFS very similar to Li2MnO3 •Co XAFS very similar to LiCoO2

The excess Li clusters predominantly around MnLocal clustering of Mn-rich and Co-rich regions

Sample and electrochemistry: Sun-Ho Kang (CSE, ANL)

24

Co-O

Co-TMMn-O

Mn-TM

Element Specific Local Structure

The excess Li clusters predominantly around Mn; charge ordering energetics important in determining short range order Local clustering of Mn-rich and Co-rich regions Mn-rich areas similar to Li2MnO3; Co-rich areas similar to LiCoO2

XAFS (In situ studies): Swati Pol

25

View of transition metal planes along [001]M

Bright-spots in image are TM columns. Li columns appear dark.Honeycomb regions (hollow core = Li column) are Li2MnO3-like. Hexagonal regions (filled core = TM column) are LiCoO2-like. No sharp boundaries between honeycomb and hexagonal regions.

Courtesy: Dan Abraham (CSE), Javier Bareno (CSE), Ivan Petrov et al., (UIUC).

Electron microscopy: Li(Li0.2Co0.4Mn0.4)O2

26

Fe and Mn K-edge : Li1.2Mn0.4Fe0.4O2

0 2 4 6 8 10 12-2

-1

0

1

2

Li1.2Mn0.4Fe0.4O2

α LiFeO2

k2 χ (k

) (Ao-

2 )

k (Ao-1)

Fe K-edge

• Mn XAFS similar to layered-Li2MnO3 •Fe XAFS similar to cubic disordered (average structure) rock-salt LiFeO2

0 2 4 6 8 10 12-2

-1

0

1

2

Li2MnO3

Li1.2Mn0.4Fe0.4O2

k2 χ (k

) (Ao-

2 )

k (Ao-1)

Mn K -edge

Studies by Naba Karan and Javier Bareno

27

In situ Cr–K edge during charge; Li[Li0.2Cr0.4Mn 0.4]O2

•Cr (III) converted to Cr(VI)35-40 % Cr(III) Cr (VI)

• Mn remains Mn (IV) and is essentially a spectator ion

Cr (III) conversion to Cr(VI) involves movement of Cr ions from octahedral sites in the layers to tetrahedral sites (outside the layers)

XRD suggests Li[Li0.2Cr0.4Mn0.4]O2 is a solid solution of LiCrO2 and Li2MnO3 (Li[Li1/3Mn2/3]O2)

Charge

Samples provided by Isobel Davidson’s group (NRC, Canada)

28

Cr –EXAFS during charge; Li[Li0.2Cr0.4Mn 0.4]O2Pristine Compound: 6 Cr-O @ ~ 1.99 Å, 6 Cr-TM @ ~ 2.89 Å

6 Mn-O @ ~1.89 Å, 4 Mn-TM @ ~2.87 ÅDistortion in TM-O clearly evident in the local scale.

Cr (VI)-O bond distance ~ 1.65 Å

Cr-O Cr-TM

Cr3+-O (blue) 1.98 ÅCr6+-O (red) 1.64 Å

29

Repeated cycling shows that the structural and electronic changes

are highly reversible , particularly after the first cycle.

Drastic reduction in FT peak heights due to conversion of Cr(III) to Cr(VI)

Analyses of EXAFS shows migration of Cr from octahedral to tetrahedral sites

Local environment starting sample similar to LiCrO2

Cr-O Cr-TM

Cr –EXAFS during charge; Li[Li0.2Cr0.4Mn 0.4]O2

30

No large changes during first 20 scans

During first 2/3rd of charge:6 Mn-O @ ~1.89 Å4 Mn-TM @ ~2.88 Å

Excess Li clustered around Mnjust as in Li2MnO3

Mn –EXAFS during charge; Li[Li0.2Cr0.4Mn 0.4]O2

Li2MnO3: Li[Li1/3Mn2/3]O2

Local regions similar to LiCrO2 (Cr-rich) and Li2MnO3 (Mn-rich) exhibit promising electrochemistry unlike micro-LiCrO2 and micro-Li2MnO3

Mn-OMn-TM

31

• Unusually, chromium has been shown to be the active metal undergoingoxidation/reduction rather than the manganese

•Manganese is essentially a spectator ion in this material

•Equally unusual are the highly reversible 3 electron oxidation/reductions, and themobility of the chromium between octahedral and tetrahedral sites

•Important structure-property relationship with regards to capacity/power fadeare being established

• Similar complex structural and electrochemical behaviour seen forLiNi0.5Mn0.5O2, Li1.2Fe0.4Mn0.4O2, LiNi1-xCr2xMn1-xO2 and LiNixCoyMn(1-x-y)O2

SUMMARY

N.K. Karan, M. Balasubramanian, D.P. Abraham, M.M. Furczon, D.K. Pradhan, J.J. Saavedra-Arias, R. Thomas, R.S. Katiyar, J. Power Sources 187 (2), 586-590 (2009).

W. S. Yoon, M. Balasubramanian, K.Y. Chung, X.Q. Yang, J. McBreen, C. P. Grey, and D.A. Fischer, “J. Am. Chem. Soc., 127 (49), 17479 –17487 (2005).

M. Balasubramanian, J. McBreen, I. J. Davidson, P. S. Whitfield, and I. Kargina, J. Electrochem. Soc. 149, A176 (2002).