facile, mild and fast thermal-decomposition reduction of

Facile, mild and fast thermal-decomposition reduction of

graphene oxide in air and its application in

high-performance lithium batteries

Zhong-li Wang, Dan Xu, Yun Huang, Zhong Wu, Li-min Wang and Xin-bo

Zhang*

State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of

Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China

1. Chemicals and Materials

Graphite powders (325 mesh, Alfa Aesar, 99.8%, AR), Potassium permanganate (KMnO4,

Aldrich Reagent, AR), Sulfuric acid (H2SO4, ≥98%, Beijing Chemical Work, AR), Phosphoric

acid (H3PO4, ≥85%, Beijing Chemical Work, AR), Hydrogen peroxide (H2O2, 30%, Aladdin

Reagent, AR), Hydrochloric acid (HCl, 36%-38%, Beijing Chemical Work, AR), Vanadium

pentoxide (V2O5, >99%, Beijing Chemical Work, AR), Ammonium persulfate ((NH4)2S2O6, ≥98%,

Xilong Chemical Work, AR), Acetylene black (Hong-xin Chemical Works),

Polyvinylidenefluoride (PVDF, DuPont Company, 99.9%), N-methyl-2-pyrrolidinone (NMP,

Aladdin Reagent, AR), Separator (polypropylene film, Celgard 2400), Electrolyte (1 M LiPF6 in

ethylene carbonate (EC)/dimethyl carbonate (DMC) with the weight ratio of 1:1, Zhangjiagang

Guotai-Huarong New Chemical Materials Co., Ltd).

2. Experimental details

2.1 Preparation of GO

Graphite oxide was synthesized by an improved Hummers method. Briefly, a 9:1 mixture of

concentrated H2SO4/H3PO4 (45:5 mL) was added to a mixture of graphite flakes (0.375 g) and

KMnO4 (2.25 g). The reaction was then heated to 50 ℃ and stirred for 24 h. The reaction was

cooled to room temperature and poured onto ice (200 mL) with 30% H2O2 (3 mL). Then, the

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2011

mixture was centrifuged (8000 rpm for 5 min). The remaining solid material was then washed in

succession with 200 mL of 30% HCl for two times, and 200 mL of water for three times. For each

wash, the mixture was centrifuged (13000 rpm for 20 min) and obtains the remaining material.

The final resulting material was freeze-dried for 24 hours to obtain graphite oxide. Graphite oxide

was further diluted in deionized water, ultrasonication for 60 min to obtain graphene oxide.

2.2 Thermal-decomposition reduction of GO in air

Solid GO sheets were obtained by frozen-dry of exfoliated GO sheets in water. After heating at

300 oC for 1h with 2 oC/min. GO sheets were decomposed into graphene. In order to optimize the

reduction conditions, different heating temperatures (200, 250, 300, 350, and 400 oC) were

investigated.

For comparison, three other methods were used to reduce graphene oxide. The first method was

thermal reduction in N2: GO was calcined in N2 at 300 oC for 1h with 2 oC/min. The second one

was thermal reduction in 5% H2/Ar: GO was calcined in H2/Ar at 550 oC for 1h with 2 oC/min.

The third one was chemical reduction by using hydrazine as reductant: 35 μL of hydrazine

solution (50% w/w) and 400 μL of ammonia solution (25% w/w) were added into 50 ml GO

solution (0.5 mg/ml) and then stirred for 1h at 95 oC.

2.3 Preparation of V2O5 nanosheets/graphene composite

In a typical synthesis of (NH4)2V6O16 nanosheets, 0.36 mg V2O5 commercial power and 4.4 g

ammonium persulfate (APS, 20 mmol) were added into 36 mL H2O. After stirring for 48 h at 50

oC, the golden-yellow precipitate was collected by centrifugation, washed thoroughly with water,

and frozen-dried. The (NH4)2V6O16 nanosheets/graphene oxide composite was prepared by

directly mixed them in water with ultrasonication for 1h and then was frozen-dried. After

treatment of the composite at 350 oC in air for 1 h, the V2O5/graphene composite was obtained.

The content of graphene in the composite was 20 wt% by the TG analysis. As a comparison, the

sample was prepared in N2 atmosphere at the same conditions.

3. Materials Characterizations

Thermogravimetric analysis (TG) was carried out using a Mettler Toledo TGA-SDTA851

analyzer (Switzerland) from 25 to 700 oC in a air flow of 80 ml/min at a heating rate of 5 oC /min.

Wide-angle X-ray diffraction (XRD) patterns were collected on Bruker D8 Focus Powder X-ray

diffractometer using Cu Kαradiation (40 kV, 40 mA). The scanning electron microscopy (SEM)


was performed by using a field emission scanning electron microscopy (FE-SEM, HITACHI

S-4800). Transmission electron microscopy (TEM) and high-resolution transmission electron

microscopy (HRTEM) images were taken on a FEI Tacnai G2 electron microscope operated at

200 kV. Atomic Force Microscopy (AFM) experiments were carried out with Veeco Instruments

Nanoscope in tapping mode. The electrical conductivity of the GO and graphene was measured by

four-point probe method (Keithely 2400). The solid samples were pressed into disk under 20 MPa

before measurement.

4. Electrochemical measurement

The positive electrodes were fabricated by mixing 80 wt% active materials, 10 wt% acetylene

black and 10 wt% PVDF binder in appropriate amount of NMP as solvent. Then the resulting

paste was spread on an aluminum foil by Automatic Film Coater with Vacuum Pump &

Micrometer Doctor Blade (MTI). After the NMP solvent evaporation in a vacuum oven at 120 ℃

for 12 h, the electrodes were pressed and cut into disks. A CR2032 coin-type cell was assembled

with lithium metal as the counter and reference electrode and polypropylene film as a separator.

The cells were constructed and handled in an argon-filled glovebox. The charge-discharge

measurements were carried out using the Land battery system (CT2001A) at a constant current

density in a voltage range of 2-4 V versus Li/Li+.

Fig. S1 Illustration of the reduction process of graphene oxide by thermal decomposition in air.

Graphene + O2 + CO + CO2 + H2O

300-350 oC

In air

Graphene oxide


Fig. S2 SEM (a), TEM (b), and HRTEM (c) images of GO; (d) TEM image of GO reduced at 300

oC for 1 h in air.

4 μm

(a)

100 nm

(b)

5 nm

(c)

500 nm

(d)


Fig. S3 AFM images of GO before (a) and after (b) reduction at 300 oC for 1 h in air.

250 nm

(b)

160 180 200 220 240 260-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

Distance (nm)

Hei

ght

(nm

)

1 nm

(b)

250 nm

0 50 100 150 200 250-1.0

-0.5

0.0

0.5

1.0

1.5

1.1 nm

Distance (nm)

Hei

ght

(nm

)

(a)


Fig. S4 X-ray diffraction (XRD) patterns of GO and reduced GO at 300 oC for 1 h in air.

10 20 30 40 50 60 70 80

Graphene

2θ (deg)

Inte

nsi

ty (

cou

nts

)

GO


Fig. S5 FT-IR (a) and Raman (b) spectra of GO before and after decomposition at 200, 300, and

400 oC for 1h in air.

4000 3500 3000 2500 2000 1500 1000 500

T

rans

mit

tanc

e (a

. u.)

Wavenumbers (cm-1)

400 oC

300 oC

200 oC

GO

(a)

1000 1200 1400 1600 1800 2000

400 oC

Raman Shift (cm-1)

300 oC

200 oC

Inte

nsit

y (a

. u.)

GO

(b)


Fig. S6 XPS spectra of C1s of GO before (a) and after (b-d) decomposition at 200, 300, and 400

oC for 1h in air, respectively. (e) XPS spectra of C1s of GO reduced at 550 oC for 1h in 5% H2/Ar.

280 282 284 286 288 290 292

Inte

nsit

y (c

ps)

Binding Energy (eV)

(a)

280 282 284 286 288 290 292

Inte

nsit

y (c

ps)

Binding Energy (eV)

(c)

280 282 284 286 288 290 292Binding Energy (eV)

Inte

nsit

y (c

ps)

(d)

280 282 284 286 288 290 292

Inte

nsit

y (c

ps)

Binding Energy (eV)

(b)

280 282 284 286 288 290 292Binding Energy (eV)

Inte

nsit

y (c

ps)

(e)


Fig. S7 The change of ID/IG and C/O ratios with temperatures during the thermal-decomposition

reduction of GO.

0 50 100 150 200 250 300 350 400 4500.7

0.8

0.9

1.0

1.1

1.2

I D/I

G

Decomposition Temprature (oC)

ID/I

G

2

3

4

5

6

C/O

C/O


Fig. S8 (a) XRD pattern of (NH4)2V6O16 nanosheets; (b) Comparison of XRD patterns of

V2O5/graphene composite prepared using different reduction method of GO.

10 20 30 40 50 60 70 80

V2O

5/Graphene in air

Inte

nsi

ty (

cou

nts

)

2θ (deg)

V2O

5-V

6O

13/Graphene in N

2

* V6O

13

**

**

(b)

10 20 30 40 50 60 70 80

(NH4)

2V

6O

16

Inte

nsi

ty (

cou

nts

)

2θ (deg)

(a)


Fig. S9 SEM images of (NH4)2V6O16 nanosheets (a) and V2O5 nanosheets/graphene (b); (c) TEM

and (d) HRTEM images of V2O5 nanosheets/graphene prepared at 350 oC in air.

The obtained (NH4)2V6O16 is very thin nanosheets with size of 10-20 nm in thickness and

several micrometers in width (Fig. S9a). After mixing with GO uniformly and heating treatment in

air, (NH4)2V6O16 nanosheets/GO is converted into V2O5 nanosheets/graphene composite and

forms sandwich-like structure (Fig. S9b and c). The lattice fringes can be observed along (110)

plane of V2O5 from the edge of an individual V2O5 nanosheets/graphene assemble (Fig. S9d).

1 μm

(a)

1 μm

(b)

200 nm

(c)

5 nm

(d)

d(110)= 0.34 nm


Fig. S10 Thermogravimetric analysis of the V2O5/graphene composite in air

atmosphere.

The weight loss of ~3% below 100 oC is probably due to the evaporation of the

absorbed moisture contents. From the TG curve, the content of graphene is ~20 wt%.

0 100 200 300 400 500 600 700 80070

75

80

85

90

95

100W

eigh

t L

oss

(%)

Temperature (oC)

20%


Fig. S11 (a) The Ragone plots of V2O5 nanosheets/graphene composite, (b) The discharge-charge

curve of the composite at the current density of 300 mA/g, (c) Electrochemical impedance spectra

of coin cell using V2O5 nanosheets/graphene composite electrode after 100 discharge-charge

cycles.

0 50 100 150 2002.0

2.5

3.0

3.5

4.0

Ele

ctro

de p

oten

tial

vs

Li (

volt

s)

Specific capacity (mAh/g)

(b)

100 1000 10000 10000010

100

1000

Ene

rgy

Den

sity

(W

h/K

g)

Power Density (W/Kg)

(a)

0 20 40 60 80 100 120 140 160 1800

-50

-100

-150

-200

Z'' (

ohm

)

Z' (ohm)

(c)


facile, mild and fast thermal-decomposition reduction of

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