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

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

cathode material

(2)

Microwave-assisted sol-gel synthesis of LiMn

_1.5

Ni

_0.5

O

₄

spinel cathode material

Hugues Duncan, Yaser Abu-Lebdeh and Isobel Davidson

ICPET, National Research Council, Ottawa ON, CANADA

(3)

Motivation

 High voltage cathode material operates at

~ 5

V

 High energy density, high power density and high cycling rates

1  Environmentally friendly, low cost

 Microwave synthesis: uniform temperature, controlled nanostructured

material

 Study of the electrolyte-cathode interface

(4)

 Modified sol-gel (Pecchini method)

1  LiMn

_1.5

Ni

_0.5

O

₄

prepared from precursors Mn(CH

₃

COO)

₂

∙4H

₂

0,

Ni(CH

₃

COO)

₂

∙ 4H

₂

0 ,LiCH

₃

COO 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 LiPF

₆

Experimental Procedure

(5)

XRD of LiMn

_1.5

Ni

_0.5

O

₄

20

30

40

50

60

70

80

90

0 20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

4:1

8:1

20:1

44:1

C

o

u

n

ts

2 Fd3m

LiMn

1.5

Ni

0.5

O

4

Glycol: Metal ratio

XRD pattern of disordered

spinel structure, Fd3m

Small amount of NiO

Sintering 730°C 3h

Glycol : Metal ratio Crystallite size

a

LiMn

_1.5

Ni

_0.5

O

₄

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

(6)

SEM

(7)

TEM

730 C 3h

100 nm

Glycol: metal ratio 44:1

Sintering temperature and time Crystallite size

a

LiMn

_1.5

Ni

_0.5

O

₄

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

(8)

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+ 7300C 8000C E vs Li + /Li / 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 / mA E vs Li+/Li / V LiMn_1.5Ni_0.5O₄ 0.1 mV/s

800°C 14h

(9)

Capacity curves

Effect of sintering temprature

0

20

40

60

80

100

0

20

40

60

80

100

120 600°C 14h

730°C 3h

800°C 14h

D

ischa

rg

e

cap

a

ci

ty

/

mAh g

-1

Cycle number

C/6

44:1 Glycol : Metal

(10)

0

10

20

30

40

50

60

70

0

20

40

60

80

100

120 4:1

8:1

20:1

44:1

D

ischa

rg

e

cap

a

ci

ty

/

mAh g

-1

Cycle number

C/6

Capacity curves

Effect of glycol:metal ratio

730°C 3h

 Similar capacity fade

44:1 ratio yield highest

(11)

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}

(12)

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 / Li}

x

PF

y

O

z

1 Shoulder at 1380 cm

-1

_{: C-H}

Shoulder at 1200 cm

-1

_{: ROM}

1700 cm

-1

_{: ROCO}

2 M / polycarbonates

(13)

Study of cathode-electrolyte interface

FTIR

1800

1600

1400

1200

1000

800

0.00

0.02

0.04

0.06

0.08

0.10

0.02

0.04

0.06

0.08 Wavelength / cm

-1

Unwashed

Washed

Comparison of electrodes washed

with DMC and unwashed electrodes

70 cycles at C/6 rate

Decrease in EC peaks

ROCO

₂

M

ROM

(14)

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 1200 0 200 400 600 800 1000 1200 Initial 3 V 3.9 V 4.34 V 4.79 V -Z '' / cm 2 Z' / cm2 1468 Hz 31.6 mHz 20 mHz

Equivalent circuit

1

(15)

Impedance spectroscopy

R

_f

stable

R

_ct

varies with potential

Both stable on cycling

0

200

400

600 800 1000 1200 1400

0

100

200

300

400

500

600

700

0

200

400

600 800 1000 1200 1400

0

100

200

300

400

500

600

700 825 Hz

4 V

1

rst

cycle

2

nd

cycle

5

th

cycle

9

th

cycle

Z' / cm

2

-Z

''

/

cm

2

Z' / cm

2

825 Hz

100 mHz

20 mHz

4.75 V

1

rst

cycle

2

nd

cycle

5

th

cycle

9

th

cycle

-Z

''

/

cm

2

(16)

Summary

 Developped a microwave-assisted synthesis of LiMn

_1.5

Ni

_0.5

O

₄

 Porous material with controllable nanosized crystallites.

 FTIR shows presence of polyether / Li

_x

PF

_y

O

_z

species on contact of

electrolyte.

 Presence of polycarbonates after prolonged cycling.

 Impedance spectroscopy confirms presence of surface layer .

 Impedance stable after first charge-discharge.

(17)

Acknowledgements

• Bryan Scheier

• Dave Kingston

, for SEM

(18)

Thank you for your attention

Questions?