Electronic Supplementary Information. A Flexible Alkaline Rechargeable Ni/Fe Battery Based on Graphene Foam/Carbon Nanotubes Hybrid Film

Transcription

1 Electronic Supplementary Information A Flexible Alkaline Rechargeable Ni/Fe Battery Based on Graphene Foam/Carbon Nanotubes Hybrid Film Jilei Liu,, Minghua Chen, Lili Zhang, Jian Jiang, Jiaxu Yan, Yizhong Huang, Jianyi Lin, Hong Jin Fan, *, and Ze Xiang Shen *, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, , Singapore Heterogeneous Catalysis, Institute of Chemical Engineering and Sciences, A*star, 1 Pesek Road, Jurong Island, , Singapore School of Materials Science and Engineering, Nanyang Technological University, , Singapore Energy Research (ERI@N), Nanyang Technological University, Singapore fanhj@ntu.edu.sg (H.J.Fan), zexiang@ntu.edu.sg (Z. S. Shen) S1

2 Materials and Methods Synthesis of Graphene Foam (GF)/Carbon nanotubes (CNTs) hybrid film. The GF/CNTs hybrid films were synthesized using a modified recipe from previous method. Briefly, the NiCo catalyst was deposited on GF via a hydrothermal process as described in previous work. The GF/NiCo precursor was then annealed in air at 350 ºC for 1 min and used directly as the catalyst-loaded substrate for the growth of CNTs at 750 ºC in a gas flow of C 2 H 4, H 2 and Ar with flow rates of 20, 40 and 100 sccm, respectively. H 2 was introduced prior to the growth process in order to activate the catalyst effectively. The areal density of GF/CNTs hybrid films was adjusted to be 0.65 mg/cm 2 in this work. Synthesis of GF/CNTs/Ni(OH) 2 hybrid film. Ni(OH) 2 nanosheets were electrochemical deposited on GF/CNTs hybrid film directly in 0.1 M Ni(NO 3 ) 2 aqueous solution at a scan rate of 100 mv/s with working windows at V (vs.sce). The mass of Ni(OH) 2 loading was controlled via adjusting the number of cyclic voltammmetry from 50 to 200. The resulting GF/CNTs/Ni(OH) 2 hybrid film was then washed thoroughly, dried, and then used as the positive electrode. The samples are denoted as GF/CNTs/Ni(OH) 2 -n, where n is the areal mass density of Ni(OH) 2 (unit of mg/cm 2 ). Synthesis of GF/CNTs/Fe 2 O 3 hybrid film. The GF/CNTs/Fe 2 O 3 hybrid film was prepared using a simple hydrothermal method as reported previously. Typically, a piece of GF/CNTs film was immersed into a mixture solution of Fe(NO 3 ) 3 9H 2 O (Merck AR, >99.0%) (with monomer amount at 1.5, 3 and 6 mm), DI water (50 ml) and 15 mmol urea (AR, >99.0%), followed by the addition of 5 ml of 30 % HCl. The mixture was then transferred into a Teflon-lined autoclave and heated at 150 ºC for 15 h. The as-prepared precursor was then washed with DI water and annealed at 550 ºC for 1.5 h in Ar to obtain GF/CNTs/Fe 2 O 3 hybrid films. The samples are denoted as GF/CNTs/Fe 2 O 3 -n, where n is mass loading amount of Fe 2 O 3 (mg/cm 2 ). Assemble of GF/CNTs/Ni(OH) 2 -GF/CNTs/Fe 2 O 3 rechargeable batteries (F-Ni/Fe batteries). Flexible Ni/Fe batteries with high performance were assembled using a piece of GF/CNTs/Ni(OH) 2 (1 4 cm 2 ) and a piece of GF/CNTs/Fe 2 O 3 (1 4 cm 2 ), with an electrolyte-soaked (6 M KOH) separator in between. The cells were fabricated using two poly(ethylene terephthalate) (PET) sheets as the flexible substrate. Materials characterizations and electrochemical measurements. Transmission electron microscopy (TEM, JEM-2010, 200 kv), field-emission scanning electron microscopy (FESEM, JEM-6700F, 10.0 kv), X-ray diffraction (XRD, Bruker D-8 Avance), X-ray photoelectron spectroscopy (XPS) on a VG ESCALAB 250 spectrometer (Thermo Electron, Altrincham, U.K) (Al K X-ray source (1486 ev)) and the N 2 adsorption/desorption (ASAP2020 volumetric adsorption analyzer (Micromeritics, USA)) were used to characterize the samples. Electrochemical measurements including galvanostatic charge/discharge curves, cyclic voltammetry (CV) curves, electrochemical impedance spectroscopy (EIS, 100 KHz-0.01 Hz) were conducted on an electrochemical workstation (CHI 760D). The S2

3 electrochemical performance of individual electrodes was investigated using a three-electrode system (Pt as the counter electrode, saturated calomel electrode (SCE) as the reference electrode) prior to the fabrication of ASCs. The software Z-View was use for EIS fitting. Calculations. The specific capacity (C*, mah/g) of positive or negative electrode in three-electrode configuration were calculated according to the equation: where I is the discharging current, m is the mass of the individual electrodes, t is the discharge time. The specific capacity (C*, mah/g) of f-ni/fe cells in two-electrode configuration were calculated according to the equation: where I is the discharging current, M is the total mass of the two electrodes, t is the discharge time. The charge balance between the positive electrode and negative electrode is obtained by the equation: C V = C + V +, where C and C + are the capacitance of negative and positive electrodes respectively, and V and V + are the potential window of negative and positive electrodes respectively. The energy density (E) and power density (P) are calculated according to the equations below: where I is the discharging current, V is the discharging voltage, differential, and m is the total mass of active materials. is the discharge time, dt is the time S3

4 Fig. S1 Electron micrograph of the GF/CNT hybrid films. (a-c) Typical FESEM images of at different magnifications and (d) corresponding TEM image. The inset in (d) is SAED pattern. S4

5 Fig. S2 FESEM images of GF/CNTs/Ni(OH) 2 hybrid films with different loading amount of Ni(OH) 2 at different magnifications. S5

6 Fig. S3 Typical TEM image (a) and HRTEM image (b) of the Ni(OH) 2 flakes in the GF/CNTs/Ni(OH) 2 hybrid electrode. The inset in (a) is the corresponding SAED pattern. S6

7 Fig. S4 FESEM images of GF/CNTs/Fe 2 O 3 hybrid films with different loading amount of Fe 2 O 3 at different magnifications. S7

8 Fig. S5 Typical TEM image (a) and HRTEM image (b) of Fe 2 O 3 mesoporous nanorod from the GF/CNTs/Fe 2 O 3 hybrid film. The inset in (a) is the corresponding SAED pattern. (c) N 2 adsorption/desorption isotherms of GF/CNTs/Fe 2 O 3 hybrid films. S8

9 Fig. S6 Electrochemical property of the GF/CNTs/Ni(OH) 2 single electrode. CV curves of GF/CNTs/ Ni(OH) hybrid film (a), Ni(OH) hybrid film (c) and GF/CNTs/Ni(OH) hybrid film (d) at various scan rates (from 2 to 50 mv/s). (b) Comparative electrochemical impedance spectroscopy. The equivalent series resistances for GF/CNTs/Ni(OH) 2-0.5, GF/CNTs/Ni(OH) and GF/CNTs/Ni(OH) are 2.9, 3.4 and 4.6 Ω, respectively. Galvanostatic discharge curves of GF/CNTs/Ni(OH) hybrid film (e) and GF/CNTs/Ni(OH) hybrid film (f) at various current densities. S9

10 Fig. S7 Electrochemical property of the GF/CNTs/Fe 2 O 3 single electrode. (a) Comparative CV curves of GF/CNTs/Fe 2 O and GF/CNTs/Fe 2 O hybrid film at a scan rate of 10 mv/s. CV curves of GF/CNTs/Fe 2 O (b) and GF/CNTs/Fe 2 O (c). (d) Galvanostatic discharge curves at various current densities of GF/CNTs/Fe 2 O hybrid electrode. (e) Comparative electrochemical impedance spectroscopy. The equivalent series resistances for GF/CNTs/ Fe 2 O and GF/CNTs/Fe 2 O hybrid film are 2.0 and 3.8 Ω, respectively. S10

11 Fig. S8 Charge balance of the two electrodes based on equation: m + C + V + = m C V Fig. S9 Variation of anodic peak current (I pa ) with scan rate for f-ni/fe cell. S11

12 Fig. S10 Electrochemical impedance spectroscopy of f-ni/fe cell. The equivalent series resistances for f-ni/fe Cell is 5.9 Ω. S12

13 Fig. S11 SEM images of (a, b) GF/CNTs/Ni(OH) 2 and (c, d) GF/CNTs/Fe 2 O 3 before and after 2,000 cycles. (e) Cycle stability. S13

14 Fig. S12 Ragone plot of f-ni/fe cell based on the total volume of device. Photographs in it show two f- Ni/Fe cells connected in series powering LEDs and a small rotation motor. S14

15 Table S1. Parameters for the flexible Ni/Fe cell (f-ni/fe Cell) and the calculated volumetric and gravimetric energy/power densities based on the fully packaged cell. Ni/Fe Cell Positive Electrode (GF/CNTs/Ni(OH) 2-0.9) Thickness ( m) Density (g/cm 3 ) Weight percentage (%) Volume Negative Electrode (GF/CNTs/Fe 2 O 3-0.6) Separator Electrolyte (6 M KOH) Percentage (%) Ni/Fe Cell E max P max E max (Wh/kg) (kw/kg) (Wh/L) Active materials (Ni(OH) 2 + Fe 2 O 3 ) Electrodes (including GF/CNTs films) P max (kw/l) Full Cell Remarks: The electrolyte is absorbed by the electrodes and thus does not take up any volume in the packaged cell. For f-ni/fe Cell: total cell mass is 20.0 mg; total volume is 36.4 L; density of packaged cell is 0.55 g/cm 3. The area density of GF/CNTs current collector is 0.65 mg/cm 2. S15

16 Table S2. Comparison of electrochemical performance of commercial supercapacitors. Company Nesscap (0300C0) Nesscap (0120C0) Nesscap (0025C0) Maxwell (BCAP3000) Maxwell (BCAP2000) ESMA (EC404) ESMA (EC401) ESMA (EC503) ESMA (EC502) ESMA (EC501) Active Electrolyte Operation C (F) Weight Volume Emax Materials Voltage (g) (ml) (Wh/kg) (V) Pmax Emax Pmax (kw/kg) (Wh/L) (kw/l) Psuedocapacitor Organic (Propylene carbonate and acetonitrile) Psuedocapacitor Organic (Propylene carbonate and acetonitrile) Carbon Organic Materials (acetonitrile) Carbon Organic material Carbon Organic material Hybrid Aqueous Hybrid Aqueous Hybrid Aqueous Hybrid Aqueous Hybrid Aqueous Remarks: Data are collected from internet web home pages of corresponding companies. S16

17 Table S3. Comparison of electrochemical performance of asymmetric supercapacitors. Ref. Active Materials 13 Ni(OH) 2 /MW NT // FeO x /graphen e 27 Ni(OH) 2 //EG O Electrolyte 38 MnO 2 //AG 1 M Na 2 SO 4 Our work Ni(OH) 2 //Fe 2 O 3 Operation Voltage (V) Current Collector 1M KOH 1.6 Nickel Foam 6 M KOH 1.8 Ultrathin Graphene foam 2.0 Nickel Foam 6 M KOH 1.6 GF/CNT s hybrid films Weight (mg) Volume ( L) Emax (Wh/kg) Pmax (kw/kg) Emax (Wh/L) Pmax (kw/l) Remarks: The calculation for Ref 13 based on data providing in Ref 13. The weight of electrolyte and separator are not included during calculation process. The data came from Ref. 27 and Ref. 38 directly. S17