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RGO/Stibnite Nanocomposites as Dual Anode for Lithium and Sodium Ion Batteries Jagadese J Vittal, Mogalahalli Venkatashamy Reddy, Bobba V.R. Chowdari, and Abdulrahman Shahul Hameed ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b01211 • Publication Date (Web): 24 Mar 2016 Downloaded from http://pubs.acs.org on March 28, 2016

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ACS Sustainable Chemistry & Engineering

RGO/Stibnite Nanocomposite as a Dual Anode for Lithium and Sodium Ion Batteries Abdulrahman Shahul Hameed,1,2 Mogalahalli Venkatashamy Reddy,3,4* Jeremiah L. T. Chen1 Bobba Venteshwara Rao Chowdari3 and Jagadese J. Vittal1** 1

Department of Chemistry, 3 Science Drive 3, National University of Singapore, Singapore

117543 2

Department of Chemistry and Earth Sciences, Qatar University, PO Box 2713, Doha, Qatar

3

Department of Physics, 2 Science Drive 2, National University of Singapore, Singapore 117542

4

Department of Materials science and engineering, 9 Engineering Drive 1, National University of

Singapore, Singapore 117576 Corresponding Authors *[email protected]; [email protected]; Telephone number: +65-65162607. Fax: +6567776126 **[email protected]: Telephone number: +65-65162975. Fax: +65-6779-1691

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ABSTRACT: RGO/Sb2S3 nanocomposite has been investigated in this study as a dual anode material for Li and Na-ion battery applications. The stibnite phase, Sb2S3 and its rGO composite have been obtained by decomposition of a molecular complex, Sb(SCOPh)3 or its rGO mixture by solid state decomposition or hydrothermal treatment. The pristine sample consists of micron sized particles with rod-like morphology while the rGO composite is made of nanoparticles of Sb2S3 embedded in rGO sheets. Electrochemical lithium and sodium storage properties of the prepared materials have been investigated using galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy studies. The rGO composite demonstrates better lithium storage capacity than the pristine sample owing to enhanced conductivity. In addition, the rGO sheets act as a buffer for volume change during lithium/sodium cycling resulting in a better energy storage. KEYWORDS: Sb2S3; graphene; anode materials; sodium ion batteries

INTRODUCTION

Lithium ion batteries (LIBs) achieved enormous commercial success in the portable electronic industry as they outperform their counterparts owing to various factors such as lightweight, compactness, design flexibility, and environmental friendliness. In recent years, the attention on LIBs grew drastically for powering electric vehicles which assists in reduction of carbon footprint, enabling greener transportation for the future. In addition, LIBs are considered as one of the prospective candidates for storage and utilization of renewable energy like wind, solar, geothermal energy, etc.1 Despite LIBs are the best proven energy storage device available in the market, high price of lithium due to its limited resources and geographical localization has


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opened up the research on Na-ion batteries as sodium is abundant in nature.2,3 More importantly, the energy storage mechanism of both batteries are similar. Graphite and other carbonaceous materials are the commonly used as anode in commercial LIBs owing to their abundance and low cost. However, its low specific capacity of 372 mAh g-1 and safety issues due to dendrite formation during charging at high rates demand the need for alternate safer anode materials with capacity higher than graphite.4 In search of better anodes,

different materials like metal oxides, sulphides, nitrides, etc., have assimilated

large interest due to their high capacity and better safety features.5-8 These materials in form of nanoparticles shows better electrochemical properties compared to bulk materials which witnessed huge increase in the preparation of nanomaterials for anode applications.5, 9-11 Various sulphides such as SnS2,12-14 MoS2,15-17 Sb2S3,18-20 Bi2S3,21-23 NiS,24 CoS2,25 etc., have been investigated as LIB anodes. They undergo reversible lithium storage via conversion mechanism, forming the corresponding metal nanoparticles embedded in Li2S matrix.6 Materials like SnS2,26,27 MoS2,28-30 Sb2S3,31-33 etc., have also been investigated as anodes for Na-ion batteries. They undergo sodium storage similar to the Li counterpart via reversible formation of metal nanoparticles embedded in Na2S matrix. Among these materials, Bi2S3 and Sb2S3 are interesting since Sb/Bi metals can undergo alloying/de-alloying reaction in addition to the conversion reaction resulting in large capacities of 626 and 946 mAh g-1 respectively. However, cycling stability of these materials have been poor due to large volume change occurring during alloying/de-alloying reaction, invoking the need for additional research. Herein, we report the synthesis of Sb2S3 and its reduced graphene oxide (rGO) composites by decomposition of a molecular complex, Sb(SCOPh)3. Electrochemical investigation of the material using galvanostatic cycling, cyclic voltammetry and EIS studies indicate its feasibility as a dual anode



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material for Li and Na-ion batteries. Presence of rGO sheets in the composite enhances the conductivity and helps to accommodate large volume change during reversible alloying reaction, resulting in better electrochemical properties.

EXPERIMENTAL

All the chemicals and solvents used in this study are commercially available and used without further purification.

SYNTHESIS OF Sb(SCOPh)3

An antimony thiobenzoate complex, Sb(SCOPh)3 was prepared at room temperature by a simple precipitation method according to literature procedure.34 Typically, 340 mg of NaOH (8.5 mmol) was dissolved in 20 mL of methanol followed by the addition of 1 mL (8.5 mmol) of thiobenzoic acid under argon atmosphere. The mixture was stirred for 10 min which resulted in an orange solution of sodium thiobenzoate (eq. 1). Subsequent addition of 654 mg (2.9 mmol) of SbCl3 in Ar atmosphere generated a cream coloured precipitate of Sb(SCOPh)3 (eq. 2) which was further stirred for 30 minutes at room temperature. The precipitate was filtered under vacuum, washed with MeOH and air-dried. Yield: 1.5 g (~100%). The resulted Sb(SCOPh)3 was used for the synthesis of Sb2S3 without further purification. 3 PhCOSH + 3 NaOH 3 Na(SCOPh) + 3 H2O

(1)

3 Na(SCOPh) + SbCl3 Sb(SCOPh)3 + 3 NaCl

(2)

SYNTHESIS OF Sb2S3 and rGO/Sb2S3


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Sb2S3 was prepared by solid state decomposition of the thiobenzoate complex at 400 oC for 6 h under continuous argon flow. The rGO/Sb2S3 composite was also prepared under similar condition by the decomposition of rGO/Sb(SCOPh)3 mixture which was obtained by stirring 50 mL graphene oxide (GO) solution (~0.1 wt %) with ~1 g of Sb(SCOPh)3 and subjecting to microwave irradiation for 10 min. The synthesis of GO has been carried out as reported earlier.3537

Attempts were also made to prepare the rGO/Sb2S3 composite by hydrothermal treatment of

the aforementioned mixture at 180 oC in 6 h in an autoclave. The rGO content in the composites was found to be ~10 % from CHNS analysis. The pristine sample and the rGO composites obtained by solid state and hydrothermal reactions will be referred as p-Sb2S3(ss), rGO/Sb2S3(ss) and rGO/Sb2S3(ht) respectively.

STRUCTURAL AND ELECTROCHEMICAL CHARACTERIZATION Powder X-ray diffraction (PXRD) patterns of the prepared materials were recorded using a Bruker D5005 or D8 Advance diffractometer employing Cu-Kα radiation. Raman spectra of the samples were recorded on a Renishaw Raman system 2000. Brunauer-Emmett-Teller (BET) surface area of the samples were determined from N2 adsorption-desorption isotherms at 77 K using Tristar 3000 (Micromeritics, USA). The samples were preheated for 2 h at 180 °C under nitrogen flow to remove any adsorbed moisture prior to the BET analysis. Thermogravimetric analysis (TGA) was carried out in N2 atmosphere with samples weighing ~5 mg at a heating rate of 5 oC min-1 using a SDT 2960 TGA thermal analyzer. Elemental analysis (CHNS) and the Inductively Coupled Plasma (ICP) analysis was carried out using an Elementar Vario Micro Cube and a Dual-view Optima 5300 DV ICP-OES system respectively. Morphology of the samples was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM micrographs of the platinum coated samples were recorded on a JEOL 5 ACS Paragon Plus Environment


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JSM-6700F ﬁeld emission scanning electron microscope (FESEM) operated at 5 kV and 10 µA while JEOL JEM 2010 (operated at 200 kV) was used to record the TEM images. Electrochemical properties of the samples were investigated using coin cells (type 2016) with Li metal foil (Kyokuto Metal Co., Japan) or Na metal (Merck) as counter electrode and glass microfiber filter (GF/F, Whatman Int. Ltd., Maidstone, England) as the separator. 1 M LiPF6 in ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) (1:1:1 v/v, Merck) was used as lithium electrolyte while 1 M NaClO4 in EC and PC (1:1 v/v) was prepared and used as sodium electrolyte. The electrodes were made from a slurry prepared by mixing active material (70 wt %) with super P carbon black (15 wt %) and PVDF binder, Kynar 2801 (15 wt %) in N-methyl pyrrolidinone (NMP) solvent.38-41 The slurry was stirred for 12 h to get a homogeneous paste and then coated onto an etched copper foil, dried at 80 oC overnight and cut into circular discs of 16 mm diameter. Coin cells were assembled in an Ar-ﬁlled glove box (MBraun, Germany) with oxygen and water concentration maintained below 1 ppm, by crimp sealing the thus fabricated anode with lithium/sodium metal as counter electrode. 38-41 The cells were aged for 8 h before they were subjected to electrochemical testing. Cyclic voltammetry and galvanostatic discharge−charge cycling studies of the cells were carried out at room temperature using computer controlled MacPile II (Bio-logic, France) and Bitrode multiple battery tester (model SCN, Bitrode, U.S.A.), respectively. Electrochemical impedance spectroscopy (EIS) measurements were carried out in the frequency range of 200 kHz to 0.001 Hz using a Solartron 1260A impedance analyzer. 38-41 RESULTS AND DISCUSSION STRUCTURE


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Thermogravimetric analysis (TGA) of Sb(SCOPh)3 and its rGO composite (shown in Figure 1) illustrate their decomposition behaviour. The TGA curves indicate a weight loss of ~60 % between 200 and 260 oC, which is associated with the decomposition of the organic ligand from the thiobenzoate complex, resulting in the formation of Sb2S3. Therefore, annealing of the complex was performed at 400 oC in argon atmosphere to obtain the desired material. The phase and purity of p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) were examined by Powder X-ray diffraction (PXRD) techniques. The PXRD patterns of p-Sb2S3, rGO/Sb2S3(ss) are shown in Figure 2b & c which reveal the formation of Sb2S3 in the orthorhombic space group, Pbnm. The diffraction peaks match well with the standard pattern of stibnite phase of Sb2S3 (JCPDS: 421393). However, elemental analysis of the samples carried out by CHNS and ICP analysis revealed the presence of additional sulphur in the final product, indicated by asterisk in the PXRD patterns. Therefore, the synthesis of rGO/Sb2S3 was carried out by liquid phase decomposition by hydrothermal reaction at 180 oC which yielded pure rGO/Sb2S3 without any additional Sulphur contamination (Figure 2d). The strong and sharp diffraction peaks indicate good crystallinity of the samples. Raman spectra of bare GO, p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) are shown in Figure 3. Bare GO (Figure 3a) exhibits the G and D bands at 1600 and 1350 cm-1 respectively while the G band in the rGO composites shifts to ~1580 cm-1 indicating the incorporation of Sb2S3 particles into the rGO layers. The ID/IG ratio of the rGO/Sb2S3 composites are also higher than the bare GO indicating the in-situ reduction of graphene oxide.

MORPHOLOGY Morphology of p-Sb2S3 and rGO/Sb2S3 composites prepared in this study were investigated using SEM and TEM. As evidenced from Figure 4a, p-Sb2S3 was obtained as 7 ACS Paragon Plus Environment


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micron sized (~10 µm) rods with small amount of additional sulphur impurity as discussed earlier which can be seen from the figure as small particles along with rods. Though p-Sb2S3 contained big particles, solid state decomposition of rGO/Sb(SCOPh)3 yielded a homogenous composite made of nanosized Sb2S3 particles embedded in rGO layers as evident from Figure 4b. The reduction of particle size of Sb2S3 in the composites compared to the pristine sample can be attributed to the presence of rGO sheets which restricts the particle growth upon annealing. The rGO layers can be seen clearly in TEM image (Figure 4c). The rGO/Sb2S3(ht) composite prepared by hydrothermal treatment of rGO/Sb(SCOPh)3 has no additional sulphur impurity and is made of nanoparticles embedded in rGO layers (Figure 3d). Porosity and BET (BrunauerEmmett-Teller) specific surface area of the pristine Sb2S3 and rGO composites were determined using N2 adsorption-desorption isotherms (Figure S1). The pristine sample exhibits poor BET surface area of 0.6 m2 g-1 owing to the large crystallite size of ~10 µm as indicated by the SEM studies. However, the rGO/Sb2S3 composites obtained by solid state decomposition and hydrothermal treatment have high surface area of 30 and 34 m2 g-1 which is expected to assist in better electrochemical properties. This high surface area can be attributed to the large surface provided by rGO sheets and the smaller particle size of Sb2S3 in the composites.

Electrochemical studies Electrochemical lithium and sodium storage properties of p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) were investigated with coin cells using galvanostatic cycling, cyclic voltammetry and EIS studies. Li and Na metal was used as the counter electrode for the lithium and sodium cycling studies respectively. The cells were subjected to charge-discharge cycling at a constant current density of 100 mA g-1 which corresponds to ~0.1 C current rate (theoretical capacity is 946 mAh g-1). 8 ACS Paragon Plus Environment

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Lithium cycling Charge-discharge profiles of rGO/Sb2S3(ss) for selected cycles in the voltage window of 0.005-3.0 V vs. Li/Li+ are shown in Figure 5a. During the initial discharge from open circuit voltage (OCV), Sb2S3 undergoes lithiation via two distinct mechanisms namely, conversion and alloying reaction at ~1.6 and 0.9 V respectively as indicated by two plateaus at these voltages. The first plateau is due to the conversion reaction of Sb2S3 with Li which results in the formation of Sb nanoparticles and Li2S (eq. 3). During this process, 6 moles of Li are consumed which corresponds to a theoretical capacity of 473 mAh g-1. The second plateau at ~0.9 V is ascribed to the consumption of additional 6 moles of Li via alloying reaction forming Li3Sb alloy (eq. 4). This process results in an additional capacity (theoretical) of 473 mAh g-1 making the total capacity as 946 mAh g-1. The overall initial discharge capacity obtained for p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) were 1386, 1511 and 1793 mAh g-1 respectively. The additional capacity, beyond the plateau region can be ascribed to the formation of solid electrolyte interface (SEI). The SEI results from the reaction of Li metal with the organic solvents present in the electrolyte. This phenomenon is commonly observed in many oxide and sulphide based anode materials like Fe2O3, ZnFe2O4, CuS, CuO, CoN etc.42-47 In addition to SEI formation, other possible reasons for the high capacity values could be polymeric layer formation and poly-sulphide dissolution etc. The excess sulphur present in p-Sb2S3 and rGO/Sb2S3(ss) did not undergo any electrochemical reaction as no plateau was observed in the discharge curve at ~2 V, characteristic of the conversion of sulphur to Li2S. Conversion reaction: Sb2S3 + 6 M ↔ 2 Sb + 3 M2S (M = Li, Na)

(3)

Alloying reaction:

(4)

2 Sb + 6 M ↔ 2 M3Sb (M = Li, Na)



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During the first charge process, de-alloying reaction of Li3Sb occurs at ~1 V, forming back Sb nanoparticles. With further increase in the voltage, Sb nanoparticles react with Li2S by conversion mechanism to form back Sb2S3 and Li. However, in p-Sb2S3 only a small plateau was observed at 1.7 V (Figure S2) followed by a sloping curve to the cut off range of 3.0 V. This indicates that the conversion of Sb to Sb2S3 is not highly feasible, limiting the first charge capacity to only 778 mAh g-1. This can be explained as the effect of large volume change occurring during the alloying/de-alloying reaction. Due to the large particle size of p-Sb2S3 the contact between Sb and Li2S particles decreases upon cycling making them partially unavailable for the conversion reaction. The rGO/Sb2S3 composites exhibit better charge capacity compared to the pristine sample indicating that the feasibility of conversion reaction is greater due to their smaller particle size and the presence of graphene layers which acts as a buffer during the volume change. Second and subsequent cycles follow the same mechanism as the first cycle resulting in reversible lithium storage. In the 2nd discharge, the plateau at 1.6 V becomes smaller indicating the decreased availability of Sb2S3 due to the incomplete conversion of Sb to Sb2S3 in the 1st charge cycle. The charge capacities of 2nd cycle obtained for p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) were 724, 895 and 1211 mAh g-1 respectively. During the subsequent cycles, the plateau at ~1 V for both the charge and discharge cycles remain almost intact, indicating the good reversibility of alloying/de-alloying reaction in the material. However, the plateau at ~1.6 V becomes shorter with increasing cycle number (Figure 5b). The capacity fading is due to the large volume expansion/contraction occurring in the electrode during the charge–discharge processes which induce mechanical stress resulting in the disintegration of the electrode from current collector.48 Slightly better capacity retention was observed for the rGO composites owing


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to increase in conductivity of the sample and the rGO layers act as buffer for the volume change and provide a better contact between Sb and Li2S particles. The rGO/Sb2S3(ht) composite exhibits higher capacity than the rGO/Sb2S3(ss) due to increased surface area and better homogeneity of the sample. However, prolonged lithium cycling results in the destruction of electrode and its loss of contact with the current collector in both rGO composites. At the end of 50 cycles, the charge capacities obtained for p-Sb2S3, rGO/Sb2S3(ss) and rGO/Sb2S3(ht) were 311, 596 and 658 mAh g-1 respectively with coulombic efficiency of ~99%. To study the effect of voltage window of the capacity retention, the rGO/Sb2S3(ht) composite was subjected to galvanostatic cycling in the range of 0.005-1.5 V vs. Li where only the alloying/de-alloying reaction is allowed. Figure 6 and and Figure S3 shows the voltage vs. capacity profiles for selected cycles at current density of 100 mA g-1. By restricting the charge voltage to the cut-off limit of 1.5 V, the conversion reaction is restricted and the material undergoes only the alloying/de-alloying reaction at ~1 V. Similar observation for better lithium cycling in the lower voltage range (0.005-1.0 V) has been reported in the literature.49-51 As seen from the capacity retention plots in the inset of Figure 6, the capacity fades slightly in the beginning and the value decreases constantly due to the disintegration of the electrode resulting in a capacity of 414 mAh g-1 after 100 cycles.

Sodium cycling The rGO/Sb2S3(ht) composite was also investigated as an anode material for sodium storage application. Figure 7a and Figure S4 illustrates the charge-discharge profiles of the material against sodium metal in the voltage window of 0.005-1.8 V vs. Na/Na+. Similar to the reaction with Li, sodium intake of Sb2S3 (discharge) undergoes via conversion reaction at ~0.9 V



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(eq. 3) followed by alloying reaction at ~0.5 V (eq. 4) as indicated by the two plateaus at these voltages. During the charge cycle, de-alloying reaction of Na3Sb occurs at 0.7 V followed by the reaction of Sb with Na2S to form Sb2S3 at 1.2-1.5 as shown by a sloping plateau. Huge capacity fading was observed with increasing cycle number due to the huge volume change which disintegrates the electrode material. The initial charge capacity of 596 decreases to 255 (40th cycle) as shown in Figure 7c. The performance is lower than reported in recent literature31 which may be explained as weak interaction between rGO and stibnite particles which could be overcome by addition of binder. When the material was subjected to Na cycling in the voltage window of 0.005-1.0 V vs. Na/Na+ (Figure 7b) where the reaction with Na conversion mechanism is restricted and only alloying reaction takes place, better capacity retention was observed. The charge capacity which was 395 mAh g-1 for the 1st cycle reduces to 306 mAh g-1 at the end of 60 cycles.

CYCLIC VOLTAMMETRY The lithium and sodium storage processes of rGO/Sb2S3 composites were also investigated by cyclic voltammetry (CV) as it gives information about the redox potentials of electrochemical reactions occurring in the electrodes. Figure 8a and 8b show the room temperature CV curves of rGO/Sb2S3 composites at a constant scan rate of 58 µV s−1 using Li and Na metal respectively as counter electrodes. As shown in figure 8a, the first cathodic scan presents two reduction peaks at 1.33 and 0.75 V vs. Li/Li+ for cycling in Li-half cells.20 For the sodiation reaction, the peaks appeared at 0.8 and 0.35 V vs. Na/Na+ (Figure 8b) similar to reported values in literature.32 The first peak in both cases is due to the lithiation/sodiation of Sb2S3 via conversion reaction, resulting in the formation of Sb nanoparticles embedded in Li2S/Na2S as per eq. 3 while the second peak is due to the alloying reaction of Sb with additional 12 ACS Paragon Plus Environment

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Li/Na forming Li3Sb/Na3Sb alloy as shown in eq. 4. In addition, the first cathodic scan presents small peaks at 1.53 V (vs. Li/Li+) and 1.2 V (vs. Na/Na+) for Li and Na cycling respectively which correspond to the intercalation of lithium/sodium into the Sb2S3 layered-structure.31 The small peaks at ~0.5 and 0.28 V in Figure 8a and b are attributed to the polysulphide dissolution from the active material.52 The redox potential for the sodiation is lower (~0.3-0.4 V) compared to the reaction with Li. During the first anodic scan (charge cycle), de-alloying reaction of Li3Sb/Na3Sb occurs at 1.05/0.75 V while the conversion reaction takes place at ~2 and 1.3 V for the Li and Na cycling respectively. The overlapping peaks for the alloying/de-alloying reaction (Figure 8a) show their good reversibility. However, area of the peak for the conversion reaction decreases upon cycling as a result of the capacity fading. This can be understood to be due to the effect of huge volume change occurring in the electrode which separates the Sb and Li2S/Na2S particles decreasing the probability of interaction between them as discussed earlier.

Electrochemical Impedance Spectroscopy (EIS) EIS measurements were carried on the rGO/Sb2S3 electrodes against lithium and sodium metal in LI and Na-half cell configurations. During each voltage change, the cells were subjected to a current density of ~100 mA g-1 and was relaxed at the given voltage for 3 h before data collection. The results are plotted as Nyquist plots (Zre vs. Zim, where Zre and Zim are respectively the real and imaginary parts of cell impedance). As shown in Figure 9a, the Nyquist plot at open circuit voltage (2.8 V) displayed a single semicircle for the Li cycling with an overall impedance of ~210 Ω. This can be explained as the combined surface film and charge transfer resistances (Rsf + Rct) and their associated capacitances (CPEsf and CPEdl) though a single semicircle was observed as it is in the high to medium frequency range. Upon reaction with lithium, the surface



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film breaks and the impedance decreases and became 74 Ω at the fully discharged state which shows relatively good conductivity of the sample. However the impedance is still high which reflects that the rGO/Sb2S3 composite may not be uniform and the rGO layers and stibnite particles are segregated. On the other hand, the reaction of Sb2S3 with Na metal in Na-half cell encounters high impedance as shown in Figure 9b. Similar to the Li- half cells, a single semicircle was observed at the open circuit voltage in the high to medium frequency range with an impedance of 696 Ω. With onset of sodium insertion, the impedance decreases to 412 Ω in the first discharge cycle at 1.0 V where the conversion of Sb2S3 to Sb and Na2S occurs. With further discharge, the impedance becomes lower and reaches 196 Ω at the fully discharged state. As shown in the figure, the prolonged sodium cycling results in increase of the impedance. The 60th cycle exhibits an impedance of 339 Ω which is almost 70 % higher than the first cycle at the particular voltage which may be attributed to the loss of contact between Sb and Na2S nanoparticles due to the huge volume change and this explains the capacity fading during prolonged cycling.

CONCLUSIONS The stibnite phase of Sb2S3 and its rGO composites were synthesized by facile decomposition of a molecular precursor, Sb(SCOPh)3 and its rGO mixture at 400 oC in argon atmosphere. The pristine sample shows inferior electrochemical performance while the rGO composite shows better lithium storage properties as rGO provides better conductivity and acts as buffer for volume change during reversible alloying of antimony. As the samples prepared by solid state decomposition has additional sulphur as impurity, the rGO/Sb2S3 was prepared via hydrothermal treatment at 180 oC which shows better electrochemical properties compared to the solid state derived samples. Reversible capacity of 658 mAh g-1 was obtained for the 14 ACS Paragon Plus Environment

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hydrothermally prepared sample after 50 cycles. As the material can undergo similar electrochemistry with Na, the rGO/Sb2S3(ht) composite was investigated as anode material in Na-half cell configuration. The cycling of the material with Na in the voltage window of 0.0051.8 V leads to severe capacity fading while restricting the cycling in the 0.005-1.0 V results in better capacity retention.

ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website at DOI: BET isotherms of p-Sb2S3 and rGO/Sb2S3, Voltage vs. capacity profiles of rGO/Sb2S3 ss and ht.

ACKNOWLEDGEMENTS JJV tanks the Ministry of Education, Singapore through NUS Tier 1 FRC grant (No. R143-000562-112). M V R would like to thank National Research Foundation (NRF) Singapore for the research Grant no. WBS:R-284-000-115-281.

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Figure 1 TGA of Sb(SCOPh)3 and rGO/Sb(SCOPh)3 in nitrogen atmosphere at a heating rate of 5 oC min-1



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Figure 2 Powder X-ray diffraction patterns of (a) JCPDS standard of Sb2S3, (b) p-Sb2S3 and (c) rGO/Sb2S3(ss) and (d) rGO/Sb2S3(ht).


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Figure 3 Raman spectra of (a) bare GO; (b) p-Sb2S3; (c) rGO/Sb2S3 (solid state) and (d) rGO/Sb2S3 (hydrothermal).



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Figure 4 (a) SEM micrograph of p-Sb2S3; (b & c) SEM and TEM images of rGO/Sb2S3(ss) and (d) SEM micrograph of rGO/Sb2S3(ht).


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Figure 5 (a) Lithium cycling studies of rGO/Sb2S3(ss) showing voltage vs. capacity profiles for selected cycles with lithium metal as anode in the voltage window, 0.005-3.0 V and (b) Comparison of capacity vs. cycle number plots of p-Sb2S3(ss), rGO/Sb2S3(ss) and rGO/Sb2S3(ht).



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Figure 6 Lithium cycling studies of rGO/Sb2S3(ht) for selected cycles with lithium metal as anode in the voltage window, 0.005-1.5 V. The inset figure shows the variation of capacity with cycle number.


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Figure 7 Sodium cycling studies of rGO/Sb2S3(ht) for selected cycles with sodium metal as anode in the voltage window, (a) 0.005-1.8 V; (b) 0.005-1.0 V and (c) variation of capacity (charge) with cycle number in different voltage ranges.



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Figure 8 Cyclic voltammograms (CV) of rGO/Sb2S3 with different anodes; (a) Lithium and (b) Sodium at a scan rate of 0.058 mV s-1


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Figure 9 Nyquist plots of rGO/Sb2S3 anodes in different half-cell configurations (a) lithium and (b) sodium



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TOC graphic

RGO/Stibnite Nanocomposite as a Dual Anode for Lithium and Sodium Ion Batteries Abdulrahman Shahul Hameed,1,2 Mogalahalli Venkatashamy Reddy,3,4* Jeremiah L. T. Chen1 Bobba Venteshwara Rao Chowdari3 and Jagadese J. Vittal1**

RGO/Stibnite composites obtained from a single molecular precursor as a dual anode material for Li-ion and Na-ion batteries


Stibnite Nanocomposite as a Dual Anode for ... - ACS Publications

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