- 1 -

Conférence internationale sur les olivines pour batteries rechargeables OREBA 1.0

In Honor of Dr. Michel Armand Montréal, May 25 – 28 2014

Margret Wohlfahrt-Mehrens

Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW) Baden-Württemberg

Lithium Metal Phosphates as Cathode Materials for Li-Ion Batteries

Status and Future Perspectives

Lithium Metal Phosphates as Cathode Materials for Li-Ion Batteries

non toxic low-cost raw materials Lower operating voltage, higher stability of electrolytes high thermal stability in the lithiated and delithiated state not a classical electrode material: •  Low electronic conductivity LiFePO4 •  Low ionic conductivity •  two-phase reaction phase boundary migration •  limited rate capability

Triphilite LiFePO4 http://www.mindat.org/photo-202039.html

LiFePO4 FePO4 + Li+ + e-chargedischarge

Padhi, A.K., Nanjundaswamy, K.S., Goodenough, J.B. Journal of the Electrochemical Society, 144 (4), 1997, 1188-1194.

Lithium Metal Phosphates as Cathode Materials for Li-Ion Batteries

Approaches to solve these problems composition and structural level nanosized material or nanostructured material building a conductive surface network - “carbon painting” Ravet, N., Chouinard, Y., Magnan,J.F., Besner, S., Gauthier, M., Armand, M., Journal of Power Sources, 97-98, 2001, 503-507N.

LiMe(II)PO4 Me(III)PO4 + Li+ + e- charge

discharge

LiFePO4 Li+ + FePO4 + e−LiFePO4 Li+ + FePO4 + e−

LiFePO4 Li+ + FePO4 + e−LiFePO4 Li+ + FePO4 + e−

Li M P O

Lithium Metal Phosphates as Cathode Materials for Li-Ion Batteries - today

inherent safe, long life, high power material

Applications •  Low voltage applications •  E-bikes •  Hybrid electric vehicles •  Electric vehicles •  Stationary applications

•  2010 – 2014 more than 1.000 scientific publications

•  initiated research on other polyanion material classes

0 3000 6000 9000 12000 150000

20

40

60

80

100

C

apac

ity /

%

Cycle number

- 5 -

Excellent Cycling Life 18650 cell Amorphous carbon//LFP

70 Wh/kg

Charge/Discharge 2C (CC)

2 – 3,6 V

Higher Safety of LFP Compared to Layered Oxides

Thermal Abuse Test

•  LFP 18650 cell: Hazard level 3 (no thermal runaway)

•  NMC 18650 cell: Hazard level 4 (thermal runaway)

LFP NMC

100 110 120 130 140 150 160 170 180 190 200 2100,0

0,5

1,0

1,5

2,0

Hea

t Rat

e [°

C/m

in]

Temperature [°C]

100 110 120 130 140 150 160 170 180

0,02

0,04

0,06

0,08

ARC

•  LFP cell: self heating is lower and shifted to higher temperature

LFP cell is more safe

Excellent Safety Compared to Layered Oxides

100 150 200 250 300 350

0,01

0,1

1

10

100

1000

SR

H [°

C/m

in]

Temperature [°C]100 150 200 250 300 350

0,01

0,1

1

10

100

1000

S

HR

[°C

/min

]

Temperature [°C]

100% SOC 30% SOC 10% SOC

100% SOC 30% SOC 10% SOC

NMC LFP

0,1

1

10

100

1000

10 30 100

SOC [%]

SHR

[°C

/min

]

0

500

1000

1500

2000

2500

Gas

Evo

lutio

n [m

l]

self-heating rate

gas evolution

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

10 30 100

SOC [%]

SHR

[°C

/min

]

0

500

1000

1500

2000

2500

Gas

Evo

lutio

n [m

l]

self-heating rate

gas evolution

LFP

NMC

0 1000 2000 3000 4000 5000 60000

20

40

60

80

100

C

apac

ity /

%

Cycle number

Routes to improve energy density: LFP//NMC Blends

0,0 0,5 1,0 1,5

0

1

2

3

4

5

Full cell Cathode Anode

Time / h

Full

cell

volta

ge /

V

and

cath

ode

pote

ntia

l / V

vs.

Li/L

i+

0,0

0,5

1,0

1,5

2,0

Anode potential / V

vs. Li/Li +

5760 cycles > 95%

NCM/LFP blend 3:1; 93% AM/ 3% CB/ 1% Gr/ 3% binder Loading: 14 mg cm-2; electrolyte EC:EMC (3:7) + 2 wt. % VC

0,0 0,5 1,0 1,5

0

1

2

3

4

5

Full cell Cathode Anode

Time / h

Full

cell

volta

ge /

V

and

cath

ode

pote

ntia

l / V

vs.

Li/L

i+

0,0

0,5

1,0

1,5

2,0

Anode potential / V vs. Li/Li +

100 150 200 250 300 350

0,01

0,1

1

10

100

1000

NMC

NMC

Blend

Blend

Temperature / °C

SH

R /

°C*m

in-1

0,0 0,5 1,0 1,5

0

1

2

3

4

5

Full cell Cathode Anode

Time / h

Full

cell

volta

ge /

V

and

cath

ode

pote

ntia

l / V

vs.

Li/L

i+

0,0

0,5

1,0

1,5

2,0

Anode potential / V vs. Li/Li +

Routes to improve energy density: LFP//NMC Blends

Charged/discharged C/5 between 3,0and 4,2 V 50 cycles 1 C CC/CD room temperature Charged C/10 to 4,2 V Maximum self heating rate NMC: 280°Cmin-1 Blend: 18°Cmin-1

From LiFePO4 to higher voltage LiMePO4 (M: Mn, Co, Ni)

130

320

145

356

187

452

010

020

030

040

050

0

spec

ific

ener

gy W

h/kg

// e

nerg

y de

nsity

Wh/

l

LFP LMP LCP

specific energy Wh/kgenergy density Wh/l

Baseline LFP 18650 cell Projected specific energy for 18650 cells assuming comparable specific capacity for manganese and cobalt based materials

•  higher energy density compared to LFP based cells •  reduce the energy density gap to layered lithium metal oxides •  increased abuse tolerance compared to layered oxides •  LCP higher capacity compared to LMNO

From LiFePO4 to LiMePO4 Me = Mn, Co Challenges and strategies

•  low electronic conductivity LiMnPO4 << LiFePO4 nanosize particles and carbon coating •  strain between charged and discharged state (lattice mismatch)

LiFePO4/FePO4 6,6% LiCoPO4/CoPO4 7,1% (intermediate phase LixCoPO4 reported)* LiMnPO4/MnPO4 9,0% generation of Jahn-Teller ion Mn3+

•  instability of the delithiated states Mn(III)PO4** and Co(III)PO4 **  LiM(1)xM(2)1-xPO4 or LiM(1)xM(2)yM(3)1-x-yPO4 for longer cycling life

•  low electrolyte stability N.N. Bramnik, K. Nikolowski, D. M.Trots, H. Ehrenberg,. Electrochemical and Solid-State Letters, 2008, 11, A89.*

S.–W. Kim., J. Kim., H. Gwon., K. Kang., J. Electrochem. Soc. 2009, 156(8), A635–A38.** L. Wang, F. Zhou, G. Ceder, Electrochem. Solid–State Lett. 2008, 11(6), A94–A96.** G. Hautier, A. Jain, S. Ong, B. Kang, C., R. Doe, G. Ceder, Chem. Mater. 2011, 23, 3495–3508**

From LiFePO4 to LiMePO4 Me = Mn, Co Challenges and strategies

LiM(1)xM(2)1-xPO4 or LiM(1)xM(2)yM(3)1-x-yPO4 for longer cycling life

3000

3500

4000

4500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1y in LiyMnxFe1-xPO4

pote

ntia

l / m

V

LiMn0.5Fe0.5PO4LiMn0.9Fe0.10PO4LiFePO4

LiMnxFe1-xPO4x = 0.0x = 0.5x = 0.9

3000

3500

4000

4500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1y in LiyMnxFe1-xPO4

pote

ntia

l / m

V

LiMn0.5Fe0.5PO4LiMn0.9Fe0.10PO4LiFePO4

LiMnxFe1-xPO4x = 0.0x = 0.5x = 0.9

solid–solution series LiMnyFe1–yPO4*, high power LiMn0.8Fe0.2PO4*

A.Yamada, S.C. Chung, J. Electrochem. Soc. 2001, 148(8), A960–A967, A. Yamada,Y. Kudo, K.–Y. Liu, J. Electrochem. Soc. 2001, 148(7), A747–A754

D. Aurbach et al. Angewandte Chemie, 2009, 121(45), 711-715

Mixed phospho olivines to compensate structural changes

Unit cell volumes of the Phospho-Olivine Phases change in the series: Mn > Fe > Co > Mg > Ni Large difference between LiMgPO4 and LiMnPO4

→ strong influence of substitution expected

Lithiated state:

solid solution of LiMnIIPO4 und LiMgIIPO4

Delithiated state –

solid solution of MnIIIPO4 and LiMgIIPO4

Δ V = 7.5%

Δ V = 3.7%

Δ V = 2.4%

Δ V = 3.5%

unit

cell

volu

me

[Å]

250 260 270 280 290 300 310

LiMnPO4 LiFePO4 LiCoPO4 LiMgPO4

Expected influence of partial substitution Consequences: smaller ΔV between charged and discharged phase → lower lattice mismatch → reduced strain at phase boundary decreasing amount of Mn(III) d4 → stabilisation of delithiated phase 1 Lithium per formula unit → lower lattice mismatch → reduced strain at phase boundary → mixed valent regions, solid solution regions

270

280

290

300

310

0,0 0,5 1,0x in LiMgxMn1-xPO4

Uni

t cel

l vol

ume

[A3]

for

solid

sol

utio

n

LMPMPlithiated state

delithiated state

Δ V

270

280

290

300

310

0,0 0,5 1,0x in LiMgxMn1-xPO4

Uni

t cel

l vol

ume

[A3]

for

solid

sol

utio

n

LMPMPlithiated state

delithiated state

Δ V

260

265

270

275

280

285

290

295

300

305

0.0 0.2 0.4 0.6 0.8 1.0x in Liy(Co1-xMnx)PO4

Ele

men

tarz

ellv

olum

en b

erec

hnet

LiCo1-xMnxPO4Li1-xCo1-xMnxPO4Co1-xMnxPO4Δ V I → II

Δ V II → III

Uni

t cel

l vol

ume

calc

ulat

ed

260

265

270

275

280

285

290

295

300

305

0.0 0.2 0.4 0.6 0.8 1.0x in Liy(Co1-xMnx)PO4

Ele

men

tarz

ellv

olum

en b

erec

hnet

LiCo1-xMnxPO4Li1-xCo1-xMnxPO4Co1-xMnxPO4Δ V I → II

Δ V II → III

260

265

270

275

280

285

290

295

300

305

0.0 0.2 0.4 0.6 0.8 1.0x in Liy(Co1-xMnx)PO4

Ele

men

tarz

ellv

olum

en b

erec

hnet

LiCo1-xMnxPO4Li1-xCo1-xMnxPO4Co1-xMnxPO4Δ V I → II

Δ V II → III

Uni

t cel

l vol

ume

calc

ulat

ed

Dynamic stability – electrochemical active M ΔV LMP/MP example Co-Mn

Step I: LiMn(II)0.5Co(II)0.5PO4 → Li0.5Mn(III)0.5Co(II)0.5PO4 + 0.5Li+ + 0.5e-

Phase I Phase II

Step II: Li0.5Mn(III)0.5Co(II)0.5PO4 → Mn(III)0.5Co(III)0.5PO4 + 0.5Li+ + 0.5e-

Phase II Phase III

Phase I Phase II Phase III

Phase I + Phase II Phase II + Phase III

ΔV I → II Δ V II → III

Effect of partial substitution on potential

LiMnPO4

2900

3100

3300

3500

3700

3900

4100

4300

4500

4700

4900

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1

x in LixMnPO4

Pote

ntia

l / m

V

LiMnPO4

LiMg0.12Mn0.88PO4

Positive potential shift ~ 150 mV

132 mAh g-1

146 mAh g-1

LiMnPO4

2900

3100

3300

3500

3700

3900

4100

4300

4500

4700

4900

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1

x in LixMnPO4

Pote

ntia

l / m

V

LiMnPO4

LiMg0.12Mn0.88PO4

Positive potential shift ~ 150 mV

132 mAh g-1

146 mAh g-1

2900

3400

3900

4400

4900

0 0,2 0,4 0,6 0,8 1y in LiyMgxFe1-xPO4

Pote

ntia

l [m

V]

LiMg0.07Mn0.83Fe0.1PO4161mAh g-1

LiMn0.5Fe0.5PO4160 mAh g-1

2900

3400

3900

4400

4900

0 0,2 0,4 0,6 0,8 1y in LiyMgxFe1-xPO4

Pote

ntia

l [m

V]

LiMg0.07Mn0.83Fe0.1PO4161mAh g-1

LiMn0.5Fe0.5PO4160 mAh g-1

LiMg0.07Mn0.83Fe0.1PO4161mAh g-1

LiMn0.5Fe0.5PO4160 mAh g-1

Mn

Fe

Co Mg (Ni, Zn)

Mn

Fe

Co Mg (Ni, Zn)

No interaction

Potential shift

•  Mg shifts Mn plateau to more positive values •  no influence on Fe plateau

Higher Oxidation States of Manganese in the Olivine Structure?

•  Li:M ratio restricts the redox-chemistry in olivines to M(II)-(III) step

•  partial substitution of Manganese fixes Li+ in the charged olivine

structure

•  in LiMnPO4, LiFePO4 and LiMnxFe1-XPO4 with and without Mg

M(II) → M(III) Li[MgII

xMnII1-x]PO4 → Lix[MgII

xMnIII1-x]PO4 + (1-x) Li+ + (1-x) e-

M(III) → M(IV) Lix[MgII

xMnIII1-x]PO4 → [MgII

xMnIVxMnIII

1-2x]PO4 + x Li+ + x e-

First discharge profile after charging to 5.3 V LMP - 7% Mg and 12%Mg

3000

3500

4000

4500

5000

5500

0 5 10 15 20 25 30

spezifische Kapazität mAh/g

Ent

lade

pote

ntia

l vs

Li/L

i+ / m

V

LMP-G18-T1 5.3 VLMP-G18-T1 5.3 VLMP-G19-T1 5.2 VLMP-G19-T1 5.2 VLMP-G18-T1 4.9 VLMP-G19-T1 4.9 V

12% Mg to 4.9 V to 5.3 V

7% Mg to 4.9 V to 5.3 V

Specific capacity [mAh/g]

Pot

entia

l vs

Li/L

i+ [

mV

]

Mn(III) → Mn(IV) + e- ?

additional potential plateau at 4.8 V !

Length depends on Mg(II) content !

Not observed for Mg substituted LFP

Formal oxidation states and electronic configurations

FeII MnII

d6 d5

FeIII MnII

d5 d5

FeIII MnIII

d5 d4

FeIV MnIII

d4 d4FeIII MnIV

d5 d3

step I

step II

step III

Li[MgxFeyMn1-x-y]PO4

Li1-y[MgxFeyMn1-x-y]PO4

Lix[MgxFeyMn1-x-y]PO4

[MgxFeyMn1-x-y]PO4

FeII MnII

d6 d5

FeIII MnII

d5 d5

FeIII MnIII

d5 d4

FeIV MnIII

d4 d4FeIII MnIV

d5 d3

FeII MnII

d6 d5

FeIII MnII

d5 d5

FeIII MnIII

d5 d4

FeIV MnIII

d4 d4FeIV MnIII

d4 d4FeIII MnIV

d5 d3FeIII MnIV

d5 d3

step I

step II

step III

Li[MgxFeyMn1-x-y]PO4

Li1-y[MgxFeyMn1-x-y]PO4

Lix[MgxFeyMn1-x-y]PO4

[MgxFeyMn1-x-y]PO4

Symmetric configurations

stabilisation of the structure

Jahn-Teller-Ions

distortion destabilisation‘ of structure

Influence of powder morphology

Li(MnFe)PO4 cycling stability

Button Cell Capacity Curves

0

20

40

60

80

100

120

140

160

0 50 100 150 200Cycle Number

Spec

ific

Cap

acity

(mAh

/g)

05-05-E05-06E06-05E06-06E07-04E07-05E07-06E08-04E08-05E10-04-E11-03-E12-03-E

Voltage range 2,5V - 4,3V, C/5 CCCV ; 1C Discharge; active mass > 92%

- 22 -

High voltage LiCoPO4 different states of charge

no exothermic reaction until the second plateau

⇒  LizCoPO4 thermal stable

⇒  exothermic decomposition of CoPO4

Enthalpy Peak B

[J/g]

Mass loss – 270°C [%]

uncharged - 0,2

24 mAh/g - 0,2

50 mAh/g - 0,3

74 mAh/g 50 0,8

120 mAh/g 79 1,0

140 mAh/g 117 1,4

Charged 163 2,4

LiCoPO4

⇓

LizCoPO4

LizCoPO4

⇓

CoPO4

0.00

0.05

0.10

0.15

0.20

0.25

0 5 10 15 20 25x in LiCo1-xMxPO4

hyst

eres

es s

tep

1 an

d 2

[V

]

Mg C1-D1Mg C2-D2Ni C1-D1Ni C2-D2Fe C2-D2Fe C1-D1

Influence of partial substitution of Co by Ni, Mg or Fe on the hysteresis of LiCoPO4

Ni

Mg Fe

-150

-100

-50

0

50

100

150

200

250

4300 4500 4700 4900 5100 5300

Potential vs Li/Li+ [mV]

dQ/d

E

C1

C2

D1

D2

Influence of electrolyte

•  Standard electrolyte without additives

•  High initial capacity, high capacity fading

•  Optimized high voltage electrolyte plus additives

•  Lower initial capacity, higher cycling stability

156 mAh/g

Optimised electrolyte solution

E. Markevich, R. Sharabi, H. Gottlieb, V. Borgel, K. Fridman, G. Salitra, D. Aurbach, G. Semrau, M.A. Schmidt, N. Schall, C. Bruenig, Electrochemistry Communications 15 (2012), pp 22-25

Calculated Energy Density of Mixed Phosphates From Measured Data

3,4 3,6 3,8 4,0 4,2 4,4 4,6 4,8 5,0110

120

130

140

150

160

170

180

LiCoPO4

LiCo0.70Mn0.15Fe0.15PO4

LiCo2/3Fe1/3PO4

LiCo1/2Mn1/2PO4

LiCo1/3Mn1/3Fe1/3PO4

LiNi0.80Co0.15Al0.05O2

LiFePO4

LiCoPO4

LiCo0.70Mn0.15Fe0.15PO4

LiCo2/3Fe1/3PO4

LiCo1/2Mn1/2PO4

LiCo1/3Mn1/3Fe1/3PO4

LiNi0.80Co0.15Al0.05O2

LiFePO4

Energy threshold NCA(refered to cathode mass only)

Rev

ersi

ble

Cap

acity

/ m

Ah/

g

Average Discharge Potential / V vs. Li/Li+

Energy threshold NCA(refered to mass of cathode and anode)

Summary

•  LFP well established safe and long life electrode material

•  Lithium mixed metal phosphates are promising as high voltage cathode materials

•  Partial substitution of Mn by other metals leads to higher stability and performance

•  Mixed Lithium Manganese Cobalt phosphates can give similar or even higher specific energy

compared with layered oxides and higher safety

•  Progressing studies of the underlying charge/discharge mechanism will lead to a deeper

understanding

•  Adjustment of composition and structure, selection of proper cell components as binder,

separator, electrolyte will lead to further breakthroughs for the high voltage materials

•  Thanks to John Goodenough and Michel Armand research directions have been

opened for new classes of materials

Peter Axmann Michaela Memm Melanie Köntje Gisela Arnold Reinhard Hemmer Wolfgang Weirather Mario Wachtler Gerda Dörfner Meike Fleischhammer Gunther Bisle

Acknowledgements

“Funktionsmaterialien und Materialanalytik zu Lithium–Hochleistungsbatterien“ WO882/4–1

BASTA

- 29 - Stuttgart Photovoltaics & Solab Energy Policy & Energy Carriers

Widderstall Solar test-field

Ulm Electrochemical Energy Technologies

Thank you for your attention!

margret.wohlfahrt-mehrens@zsw-bw.de www.zsw-bw.de

Zentrum für Sonnenenergie- und Wasserstoff-Forschung

Baden-Württemberg Helmholtzstraße 8, 89081 Ulm

Ulm eLab Center for battery research

100 200 300 400 500

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,0

0,1

DS

C [m

W/m

g]

Temperature [°C]

0

5

10

15

20

25

m/z

= 32

and

44,

Ion

curr

ent [

10-1

0 A]

100 200 300 400 500

-0,4

-0,3

-0,2

-0,1

0,0

0,1

0,2

0,3

DS

C [m

W/m

g]

Temperature [°C]

0,00

0,02

0,04

0,06

0,08

0,10

m/z

= 32

and

44,

Ion

curr

ent [

10-1

0 A]

High-Voltage LiMnPO4: Effect of Doping

A

B

exo.

CO2 (m/z=44)

O2 (m/z=32)

C

A

B

CO2 (m/z=44)

O2 (m/z=32)

C 4,8V 4,8V

•  Exothermic Reaction B: 335°C •  CO2-Formation: 335°C •  No O2-Formation

Heat formation decreases

LiMnPO4 Mg-doped LiMnPO4

Electrolyte: 1Mol LiPF6 EC:DMC= 1:1

37J/g

19J/g

•  Chemical composition •  Crystal structure •  Doping •  SEI stability

Thermal Stability of Fully Charged Cathode Materials From Layered Structure to Olivine

100 200 300 400 500

-0,1

0,0

0,1

0,2

0,3

0,4

0,5

DS

C [m

W/m

g]

Temperature [°C]

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

6,0

m/z

= 32

, Ion

cur

rent

[10-1

0 A]

A

B

A

C

Li(Ni1/3Mn1/3Co1/3)O2 (NMC) LiFePO4 (LFP) 4,3V 4,2V

exo.

•  Exothermic Reaction: 250-500°C •  O2-Formation: 300°C Structural changes:

R-3m-type → NiO-type + O2

•  Only small Exothermic Reaction: 470°C •  CO2-Formation: 470°C (→ binder reaction) •  No O2-Formation

CO2 (m/z=44)

O2 (m/z=32) O2 (m/z=32)

100 200 300 400 500

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,0

DS

C [m

W/m

g]Temperature [°C]

5

10

15

20

25

30

m/z

= 32

and

44,

Ion

curr

ent [

10-1

0 A]

Electrolyte: 1Mol LiPF6 EC:DMC= 1:1

0

20

40

60

80

100

0 2000 4000 6000 8000 10000 12000Cycle

rela

tive

Capa

city

[% o

f ini

tial]

- 32 -

Excellent Cycling Life 18650 cell Amorphous carbon//LFP

70 Wh/kg

Charge/Discharge 2C (CC)

2 – 3,6 V