Electronic Supplementary Material (ESI) for ChemComm. This journal is The Royal Society of Chemistry 2014 Supporting Information An Interlaced Silver Vanadium Oxide-Graphene Hybrid with High Structural Stability for Use in Lithium Ion Batteries Jiwen Qin a, Wei Lv a, Zhengjie Li b, Baohua Li a*, Feiyu Kang a and Quan-Hong Yang a,b* a Engineering Laboratory for Functionalized Carbon Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; yang.quanhong@sz.tsinghua.edu.cn; libh@sz.tsinghua.edu.cn. b Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China; qhyangcn@tju.edu.cn. 1. Sample preparation Graphite oxide was prepared from nature flake graphite by a modified Hummers method. As prepared graphite oxide was then dispersed in deionized water to obtain a homogeneous graphene oxide (GO) hydrosol by ultrasonication (200 W, JY92-N, a high-energy bench mounted ultrasonic disintegrator) for 2 h. The SVO-graphene hybrids were prepared by a facile hydrothermal approach under the reaction of AgNO 3 with NH 4 VO 3 in the presence of GO in a Teflon-lined autoclave. In a typical procedure, AgNO 3 (170 mg) was dispersed in 40 ml GO hydrosol (1 mg ml -1 ) by a sonication for 1 h to obtain a homogenous mixed dispersion. At the same time, NH 4 VO 3 (117 mg) was dissolved in 40 ml deionized water and heated at 80 C with consecutive stirring until the color of solution became pale yellow. Then, the NH 4 VO 3 solution was slowly added to the above mixed dispersion under ultrasonication with the ph value of about 2.5~2.7. In order to mix it uniformly, another one hour sonication was conducted. After that, the final mixture suspension was transferred into a 120 ml autoclave and heated in an oven at 180 C for 12 h, and the obtained product was collected by centrifugation at 8000 rpm for 10 min and washed with ethanol and deionized water for at least 4 times. Finally, the SVO-graphene hybrid (also denoted as ) was obtained after being freeze-dried for 36 h. In order to investigate the influence of GO contents on the structure and electrochemical 1
performance, the concentration of GO hydrosol was changed to 0.5 mg ml -1, 1 mg ml -1, 2 mg ml -1 and 3 mg ml -1, and the obtained samples were denoted as the SVO-graphene (20), (simply denoted as SVO-graphene in the manuscript), SVO-graphene (80) and SVO-graphene (120) according to the weight of GO added. A control sample was prepared under the same condition without the introduction of GO. 2. Characterization The morphology and structure of the obtained samples were characterized by field emission scanning electron microscopy (SEM, Hitachi S-4800) equipped with an energy-dispersive X- ray spectroscopy, transmission electron microscopy (TEM, JEOL, JEM-2100F) at an accelerating voltage of 200 kv and X-ray diffraction (XRD, Rigaku D/max 2500/PC using Cu Kα radiation, λ=1.5418å). Atomic force microscopy (AFM) image was obtained on Dimension Icon (ScanAsyst, Bruker). Raman spectra were recorded with a LabRAM HR800 (Horiba) using 532nm incident radiation. The X-ray photoelectron spectroscopy (XPS) characterization of the products was performed on an Axis Ultra photoelectron spectrometer using an Al Kα (1486.7 ev) X-ray source. 3. Electrochemical measurements The electrochemical properties of the SVO-graphene hybrids were studied as the active material in coin cells. The cathode electrodes were composed of 80 wt% active material, 10 wt% acetylene black and 10 wt% polyvinylidene fluoride (PVDF). A solution (1 M) of LiPF6 in EC/DEC (1:1 v/v) was used as the electrolyte. The cells were assembled in an argon-filled glove box. Galvanostatic charge/discharge measurement was performed by a multichannel battery testing system (LAND CT2001A) in the voltage range of 1.5 V~3.7 V. Cycling voltammetry (CV) were tested with an electrochemical workstation (VMP3, Bio-Logic, France) with a voltage range from 1.5 V to 3.7 V at a scan rate of 0.1 mv/s. The electrochemical impedance spectroscopy (EIS) was carried out with the frequency range from 2
100 khz to 10 mhz on the electrochemical workstation (VMP3, Bio-Logic, France) by applying a 5 mv of AC oscillation. All the measurements were carried out at room temperature. 4. Supplementary Figures Fig. S1 AFM image of GO sheet after mixed with AgNO 3 and the inset height profile shows the thickness of the GO is about 1.2 nm. (a) Fig. S2 Typical SEM image of the pure SVO without graphene. 3
Percentage (wt %) 100 95 90 85 6% 80 100 200 300 400 500 600 T ( ) Fig. S3 TG curve of the hybrid (simply denoted as SVOgraphene in the manuscript). 1 h (a) 4 h 12 h Fig. S4 TEM and HRTEM image of the hybrid synthesized in 12 h. The HRTEM of hybrid shows a well-defined crystalline structure with a lattice space of 0.29 nm, corresponding to the (003) plane of Ag 1- x. 4
Ag Ag 1-x 24 h 12 h 8 h 4 h 2 h 1 h 20 30 40 50 60 70 80 2θ (degree) Fig. S5 XRD patterns of the hybrids hydrothermally treated with different time. 4.0 3.5 (a) 4.0 3.5 Voltage (V) 3.0 2.5 2.0 Voltage (V) 1.5 5 th 4 th 3 rd 2 nd 1 st 1.0 0 50 100 150 200 250 300 350 1.0 0 50 100 150 200 250 300 350 Specific capacity (mah g -1 ) Specific capacity (mah g -1 ) Fig. S6 The first 5 discharge-charge curves of (a) the pure SVO without graphene and the hybrid at 50 ma g -1 over a potential window of 1.5 V-3.7 V vs. Li/ Li +. 3.0 2.5 2.0 1.5 5 th 4 th 3 rd 2 nd 1 st 5
Fig. S7 Typical SEM image of the hybrid electrode material after 50 cycles. SVO(Ag 1-x )/graphene (120) SVO(Ag 1-x )/graphene (80) SVO(Ag 1-x )/graphene (40) SVO(Ag 1-x )/graphene (20) SVO without graphene (Ag 2 V 4 O 11 ) 10 20 30 40 50 60 70 80 2θ (degree) Fig. S8 XRD patterns of the pure SVO without graphene and the SVO-graphene hybrids with different contents of GO. The formation of Ag 1-x after graphene added is possibly due to some Ag + were reduced into Ag, resulting in the amount of Ag + that participates in the formation of SVO is insufficient. 6
Specific capacity (mah g -1 ) 350 300 250 200 150 100 50 200 ma g -1 SVO prepared from 0 10 20 30 40 50 Cycle number Fig. S9 The comparison of the electrochemical performance of and SVO prepared by the removal of graphene from through calcining it in air at 450 C for 2 h. 1 h 2 h 4 h 8 h 12 h 24 h 1000 1200 1400 1600 1800 Raman shift (cm -1 ) Fig. S10 Raman spectra of the hybrid prepared in different hydrothermal treatment time. 7
(a) mixture of SVO and graphene mixture of SVO and graphene p C 1s 526 524 522 520 518 516 514 512 510 Binding Energy (ev) 290 288 286 284 282 280 Binding Energy (ev) Fig. S11 (a) p and C 1s XPS profiles of hybrid and a simple mixture of SVO and graphene. Specific capacity (mah g -1 ) 500 450 400 350 300 250 200 150 100 50 (a) 50 ma g -1 V 0 0 10 20 30 40 50 Cycle number SVO-graphene (20) SVO-graphene (80) SVO-graphene (120) Specific capacity (mah g -1 ) 500 450 400 350 300 250 200 150 100 50 200 ma g -1 SVO-graphene (20) SVO-graphene (80) SVO-graphene (120) 0 0 10 20 30 40 50 Cycle number Fig. S12 The comparison of the cycling behavior of the SVO-graphene hybrids added with different content of GO: 20 mg, 40 mg, 80 mg, 120 mg at (a) 50 ma g -1, 200 ma g -1 with a potential window of 1.5V-3.7 V vs. Li/ Li +. 8
(a) (c) Fig. S13 Typical SEM images of the SVO-graphene hybrids prepared by adding different contents of GO: (a) 20 mg, 80 mg, (c) 120 mg. SVO-graphene (20) SVO-graphene (80) SVO-graphene (120) 1000 1200 1400 1600 1800 Raman shift (cm -1 ) Fig. S14 Raman spectra of the SVO-graphene hybrids with different contents of GO. -Z'' (Ω) 600 400 200 SVO-grphene (20) SVO-grphene (40) SVO-grphene (80) SVO-grphene (120) 0 0 100 200 300 400 500 Z' (Ω) Fig. S15 EIS profiles of the SVO-graphene hybrids with different contents of GO. 9