Electronic Supplementary Information (ESI) for

Facile hydrothermal synthesis of CuFeO2 hexagonal platelets/rings and

graphene composites as anode material for lithium ion batteries

Yucheng Dong,a,b* Chenwei Cao,b Ying-San Chui, a,b Juan Antonio Zapien a,b*

aCenter of super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong KongbDepartment of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue,

Kowloon, Hong Kong SAR, PR Chinac* E-mail: yc-d@hotmail.com, apjazs@cityu.edu.hk

Experimental Section

Synthesis of graphene oxide

Graphene oxide (GO) was prepared from natural graphite powder according to a modified

Hummers’ method.1 First, the graphite powder was oxidized using 0.9 g NaNO3 and 37 mL of

concentrated H2SO4 that were added to 1 g graphite powder cooled in an ice bath. This mixture

was continuously stirred while 5 g of KMnO4 was added slowly over 1 h. It was left to stir for 2

h in the ice bath, and then removed and left for 4 days under continuous stirring. A black viscous

liquid was obtained and 100 mL of deionized water was added over 30 min while stirring

continuously. The mixture was stirred for a further 2 h, 10 mL H2O2 (30wt% aqueous solution)

was slowly added and then the mixture was left to stir for another 2 h. The resulting oxidized

material was washed three times by 10wt% diluted hydrochloric acid and then washed by

deionized water till the pondus hydrogenii (pH) value was close to 7. A light yellow GO powder

was obtained after freeze drying for 12 h.

Preparation of Cu-CuFe2O4/G composites

In a typical synthesis, 250 mg GO was dissolved in 30 mL deionized water by sonication for 1 h,

0.1 mol NaOH was added into the resulting solution with stiring and subsequently sonication for

1 h. Next, 0.005 mol Fe(NO3)3.9H2O and Cu(NO3)2.3H2O were dissolved in 10 mL deionized

water, and then added into the prepared GO and NaOH mixed suspension dropwise with stirring,

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2014

followed by sonication for 30 min and further stirring for 30 min. 0.5 mL of propionaldehyde

was added into the suspension as a reducing agent. Then, the suspension was transferred to an

autoclave (50 mL) and heated at 180 oC for 24 h. After cooling down to room temperature, the

product was centrifuged and washed several times by alcohol and deionized water before drying

at 60 oC for 12 h. For comparison, the pure CuFeO2 crystals were prepared under the same

experimental conditions except without GO. And graphene as an anode material was prepared by

hydrazine hydrate reduced GO.

Characterization

The structure of the products were characterized using X-ray diffraction (XRD, Philips PW

1830). Raman spectroscopy (Renishaw 2000, Raman microscope with 633 nm argon ion laser)

was employed to verify chemical bonding characteristics of graphene. The morphology was

investigated by scanning electron microscopy (SEM; Philips, XL 30FEG), transmission electron

microscopy (TEM; Philips, CM20 operated at 200kV), and high-resolution TEM (HRTEM;

CM200 FEG operated at 200kV).

Electrochemical measurements

The electrochemical measurements were performed using coin cells (2032) with lithium foil

(Aldrich, USA) as the counter electrode. The working electrodes were prepared by mixing

70wt% active material (CuFeO2/G composites), 20wt% acetylene carbon black, and 10wt%

polyvinylidene fluoride (PVDF) binder dissolved in 1-methyl-2-pyrrolidinone (NMP) solvent to

form slurry, which was homogeneous coated on copper foil and dried at 100 oC for 10 h in a

vacuum oven. Circular (1.6 cm2) anode discs were punched from the copper foil and weighed to

determine the amount of active material before assembleing into coin-type cells using layer of

Celgard 2032 (Celgard, Inc., USA) as the separator. The typical mass load of the active mateiral

is about 0.98 mg cm-2. The electrolyte was prepared from LiPF6 (1 mol L-1) dissolved in ethylene

carbonate/dimethyl carbonate (EC:DEC=1:1, v/v). Cyclic voltammograms (CV) were conducted

on a CHI-660C electrochemical workstation. Electrochemical impedance spectroscopy (EIS) was

carried out on a ZAHNER-elektrik IM6 over a frequency range of 100 kHz to 5 mHz.

Galvanostatic discharge/charge cycling measurement was performed on an Arbin Instruments

(BT 2000, College Station, Texas, USA) battery test system at various C rates (1 C=708 mA g-1)

between 5 mV and 3 V versus Li+/Li.

Fig. S1 SEM images of CuFeO2/G composites with different magnifications.

Fig.S2 SEM images of (a) 25 mg GO and (b) 0.4 g NaOH was added into the presursor solution,

respectively, while keeping other experiment conditions the same.

Fig. S3 Galvanostatic discharge-charge voltage profiles of CuFeO2/G composites for the first

three cycles between 0.005 and 3 V (vs Li+/Li) at a current density of 100 mA g-1.

Fig. S4 Cyclic stability of CuFeO2/G composites tested at a current rate of 1 C for 100 cycles.

Fig. S5 SEM images of CuFeO2/G composites after 100 cycles at the current rate of 0.2 C.

1 W.S. Hummers and R.E. Offeman, J.Am. Chem. Soc., 1958, 80,1339.