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Microwave-assisted sol-gel synthesis of LiMn1.5Ni0.5O4 spinel cathode materialDuncan, Hugues; Abu-Lebdeh, Yaser; Davidson, Isobel

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Microwave-assisted sol-gel synthesis of LiMn1.5Ni0.5O4

spinel cathode material

Hugues Duncan, Yaser Abu-Lebdeh and Isobel Davidson

ICPET, National Research Council, Ottawa ON, CANADA

Motivation

High voltage cathode material operates at ~ 5V

High energy density, high power density and high cycling rates1

Environmentally friendly, low cost

Microwave synthesis: uniform temperature, controlled nanostructured

material

Study of the electrolyte-cathode interface

1. S. Niketic et al., Meet. Abstr. – Electrochem. Soc. 801 (2008) 155

Modified sol-gel (Pecchini method)1

LiMn1.5Ni0.5O4 prepared from precursors Mn(CH3COO)2∙4H20,

Ni(CH3COO)2 ∙ 4H20 ,LiCH3COO in the required stochiometries are

dissolved in ethylene glycol; addition of citric acid.

Microwave step: 175 C, 20 min.

Resulting gel fired in stainless beaker.

Sintering step, 600 C – 800 C 3h-14h.

65% active material, 10% KS-4, 10% Super S, 15% PVDF binder

Electrolyte: 3:7 EC:DEC 1M LiPF6

Experimental Procedure

1. M. Kunduraci and G.G. Amatucci, J. Electrochem. Soc. 153 (2006) A1345-1352

XRD of LiMn1.5Ni0.5O4

20 30 40 50 60 70 80 900

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

4:1

8:1

20:1

44:1

Co

un

ts

2

Fd3m

LiMn1.5

Ni0.5

O4

Glycol: Metal ratio

XRD pattern of disordered

spinel structure, Fd3m

Small amount of NiO

Sintering 730°C 3h

Glycol : Metal ratio Crystallite size a LiMn1.5Ni0.5O4 NiO

nm Å % %

4:1 122.8 8.18 97.9 2.1

8:1 104.7 8.1719 98.2 1.8

20:1 87.1 8.183 99.1 0.9

44:1 102 8.1796 98.9 1.1

SEM

Porous aggregates of several microns

TEM

730 C 3h

100 nm

Glycol: metal ratio 44:1

Sintering temperature and time Crystallite size a LiMn1.5Ni0.5O4 NiO

nm Å % %

600°C 14h 44.6 8.1739 99.3 0.7

730°C 3h 102 8.1796 98.9 1.1

800°C 14h 173.6 8.1726 97.9 2.1

50 nm

600 C 14h

Charge-discharge curves

0 10 20 30 40 50 60 70 80 90 100

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

Ni3+

--> Ni4+

Ni2+

--> Ni3+

7300C800

0C

E v

s L

i+/L

i /

V

Capacity / mAh g-1

6000C

Mn3+

--> Mn4+

3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

I / m

A

E vs Li+/Li / V

LiMn1.5

Ni0.5

O4

0.1 mV/s

800°C 14h

Capacity curves

Effect of sintering temprature

0 20 40 60 80 1000

20

40

60

80

100

120

600°C 14h

730°C 3h

800°C 14h

Dis

cha

rge

cap

acity / m

Ah g

-1

Cycle number

C/6

44:1 Glycol : Metal

0 10 20 30 40 50 60 700

20

40

60

80

100

120

4:1

8:1

20:1

44:1

Dis

cha

rge

cap

acity / m

Ah g

-1

Cycle number

C/6

Capacity curves

Effect of glycol:metal ratio

730°C 3h

Similar capacity fade

44:1 ratio yield highest

capacities

Study of cathode-electrolyte interface

FTIR

1800 1600 1400 1200 1000 800

Wavelength number / cm-1

EC

DEC

EC:DEC 3:7 1 M LiPF6

ATR mode

Regions:

1800 – 1700 cm-1: C=O

1600 – 1400 cm-1: C-H

1300 – 1000 cm-1: C-O

845 cm-1: P-F

1800 1600 1400 1200 1000 800

Wavelength number / cm-1

24h storage

15 cycles

130 cycles

Study of cathode-electrolyte interface FTIR

Unwashed electrodes

Peaks of EC, P-F

New peaks:

1285 cm-1: polyethers / LixPFyOz1

Shoulder at 1380 cm-1: C-H

Shoulder at 1200 cm-1: ROM

1700 cm-1: ROCO2M / polycarbonates

1. T. Eriksson et al., J. Electrochem. Soc. 149 (2002) A69-A78

Study of cathode-electrolyte interface FTIR

1800 1600 1400 1200 1000 8000.00

0.02

0.04

0.06

0.08

0.10

0.02

0.04

0.06

0.08

Wavelength / cm-1

Unwashed

WashedComparison of electrodes washed

with DMC and unwashed electrodes

70 cycles at C/6 rate

Decrease in EC peaks

ROCO2M

ROMLixPyFOz

Study of cathode-electrolyte interface

Impedance spectroscopy

Swagelock-type cell

Li reference

Formation of layer on

contact of electrolyte

1. Aurbach et al., J. Electrochem. Soc, 147 (2000) 1322

0 200 400 600 800 1000 12000

200

400

600

800

1000

1200

Initial 3 V

3.9 V

4.34 V

4.79 V

-Z''

/ c

m2

Z' / cm2

1468 Hz

31.6 mHz

20 mHz

Equivalent circuit1

Impedance spectroscopy

Rf stable

Rct varies with potential

Both stable on cycling

0 200 400 600 800 1000 1200 14000

100

200

300

400

500

600

700

0 200 400 600 800 1000 1200 14000

100

200

300

400

500

600

700

825 Hz

4 V 1rst

cycle

2nd

cycle

5th cycle

9th cycle

Z' / cm2

-Z''

/ c

m2

Z' / cm2

825 Hz

100 mHz

20 mHz

20 mHz

4.75 V 1rst

cycle

2nd

cycle

5th cycle

9th cycle

-Z''

/ c

m2

Summary

Developped a microwave-assisted synthesis of LiMn1.5Ni0.5O4

Porous material with controllable nanosized crystallites.

FTIR shows presence of polyether / LixPFyOz species on contact of

electrolyte.

Presence of polycarbonates after prolonged cycling.

Impedance spectroscopy confirms presence of surface layer .

Impedance stable after first charge-discharge.

Acknowledgements

• Bryan Scheier

• Dave Kingston , for SEM

• Dr Dashan Wang, for TEM

Thank you for your attention

Questions?