Supporting Information. High performance flexible solid-state supercapacitor with extended nano

Transcription

1 Supporting Information High performance flexible solid-state supercapacitor with extended nano regime interface through in situ polymer electrolyte generation Bihag Anothumakkool* 1,3, Arun Torris A T 2, Sajna Veeliyath 1,4, Vidyanand Vijayakumar 1,3, Manohar V Badiger* 2,3 and Sreekumar Kurungot* 1,3 1 Physical and Materials Chemistry Division and 2 Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Pune , Maharashtra, India. 3 Academy of Scientific and Innovative Research (AcSIR), Anusandhan Bhawan, 2 Rafi Marg, New Delhi , New Delhi, India. 4 Department of Applied Chemistry, Cochin University of Science and Technology, Cochin , Kerala, India bihagkottuvatta@gmail.com, mv.badiger@ncl.res.in, k.sreekumar@ncl.res.in S-1

2 Experimental section: Materials: Activated carbon (YP-80F) was procured from Kuraray Chemical Co., Japan. Conducting carbon filler was purchased from Alfa Aesar. Polyvinylivene Fluoride used in the study was Kynar PVDF and this was procured from Global Nanotech. N-methylpyrrolidone and hydroxyethylmethacrylate (HEMA) monomer (MW:130.15) were purchased from Fluka and trimethylolpropaneallyl ether (TMPAE) monomer (MW:172.24) was purchased from Aldrich Chemicals. 2-Hydroxy-2-methylpropiophenone (HMPP), concentrated H 3 PO 4 and polyvinyl alcohol (PVA) (MW:1,15,000) were purchased from Loba Chemie Pvt. Ltd. Polypropylene membrane procured from Celgard was used as the separator. Grafoil, used as current collector, was procured from the GrafTech. Preparation of the electrode: Activated carbon, conducting carbon and Kynar PVDF were made into a paste with N-methylpyrrolidoneine with a ratio of 80:15:5. It was then kept for stirring for about 6 h. This was followed by probe sonication for about half an hour and the slurry was then coated over the grafoil sheet using bar coater. The carbon coated grafoil sheet was then dried in the oven at 80 o C for overnight. The grafoil electrode was pressed at 80 C using a hot press. It was followed by overnight drying at about 180 C. Similarly, the carbon coated grafoil electrodes having different thicknesses or of different loading of the material were prepared by adjusting the coating thickness. Preparation of the gel electrolyte: A mixture of HEMA, TMPA and H 3 PO 4 were used for making the gel electrolyte in presence of the UV initiator, HMPP. For comparison, gels were also prepared using HEMA and H 3 PO 4 and without the presence of cross linker. In a typical synthesis, HEMA and TMPA monomer ratio is kept as 2:1 and further the amount of H 3 PO 4 was varied. A 2 ml vial containing the above mixture was cured under UV light for about 20 minutes. Preparation of the PVA- H 3 PO 4 solution: To prepare a 10 weight percentage PVA solution, approximately 1 g of PVA was weighed and added into an RB flask containing 10 ml deionised water. The mixture was subsequently heated at 80 o C with constant stirring until a clear solution of PVA was obtained. The solution was then cooled to room temperature and the desired amount of phosphoric acid (H 3 PO 4 ) was added. It was then stirred for about 30 min. for thorough mixing. Solid-state Device fabrication: After various trials of different combinations, a ratio of 25:12.5:62.5 was fixed for HEMA, TMPA and H 3 PO 4 respectively by considering the conductivity and physical properties of the derived materials. The above monomer mixture, S-2

3 acid and UV initiator were mixed together and dropped onto 4 cm 2 area (12 cm 2 for the flexible capacitor) of the carbon coated grafoil sheets and this was kept for 3 h in idle condition. Two such electrodes were prepared in the same manner and were sandwiched together by keeping a polypropylene membrane followed by sealing with the help of sellotape along the edges to prevent solvent leakage. This was followed by curing under UV light for about 20 minutes. After the gel formation, the sellotape sealing was removed. In case of the devices using PVA- H 3 PO 4, 62.5 % H 3 PO 4 was added to the PVA water solution. Carbon electrodes were soaked in this solution, and were sandwiched together by keeping a separator in between after the evaporation of excess water from the polymer. Electrochemical Characterization: All the electrochemical studies were carried out in a BioLogic SP-300 Potentio-Galvanostat. Adhesive copper tape was used for making contacts. Cyclic Voltammetry (CV) measurements were taken at different scan rates from 10 to 500 mv/s by maintaining a potential window in the range of 0 to 1.0 V. The charge-discharge measurement was carried out at different current densities from 1 to 20 ma/cm 2. Cycling stability was monitored by using chrono charge-discharge at a current density of 5 ma/cm 2 for many thousand cycles. For comparison, devices also were made in a similar fashion as that of the solid devices without removing the sealing in order to keep the electrolyte confined. 0.5 M H 2 SO 4 and 1 M TEABF 4 /PC were used as the electrolytes for this purpose. Mass/areal/volumetric specific capacitance was calculated from the chrono charge-discharge method using the following general equation: C = 2 x ( IΔt ΔV M/V/A ) (1) where Δt = Discharge time ΔV = Potential window I = Constant current used for charging and discharging M = Weight of active carbon material in the electrode V = Volume of the carbon film on the electrode A = Area of the single electrode Multiplication with a factor of 2 was needed in the above equation in order to convert the capacitance of the device into the capacitance of the single electrode. Calculation of the columbic efficiency has been done from the charge-discharge cycling by taking the percentage of the charging time coulombs by the discharge coulombs. S-3

4 Gravimetric energy density (E d ) and power density (P d ) were calculated from the capacitance value obtained from the charge-discharge method. Energy density (E d (Wh/kg)) = 1 C 8 sv where, C s is the specific capacitance calculated by the charge-discharge (F/g) method Power density (P d (W/kg)) = E t where, V is the voltage window and t is the discharge time in hour calculated from the discharge curve. Electrochemical impedance (EIS) analysis was carried out from 10 6 Hz to 0.01 Hz frequency against the open circuit potential with a sinus amplitude of 10 mv (Vrms = 7.07 mv). The analysis of the EIS data was done by using an EC-Lab Software V Further, the spectrum was fitted using an equivalent circuit as shown below and the ESR of the devices was taken as Rs value of the equivalent circuit. Circuit S1: The equivalent circuit used fitting the impedance spectra. Conductivity measurements: Conductivity of the gel films was measured by keeping them between two stainless steel discs and connecting through crocodile clips. The x-intercept of the Nyquist plot is taken as the bulk resistance of the membrane and the conductivity can be measured by using the equation: ρ = RA l (2) where, σ = 1 ρ (3) σ= Conductivity of the membrane ρ = Resistivity of the membrane R = bulk resistance of the membrane A = Area of the membrane l = Thickness of the membrane Characterisation: Structure and morphology of the materials were analyzed with the help of a Nova Nano SEM 450 and Quanta Scanning Electron Microscope. High-resolution S-4

5 transmission electron microscope (HR-TEM) analysis was carried out in Tecnai-T 30 by using an accelerated voltage of 300 kv. Nitrogen adsorption-desorption experiments were conducted at 77 K using Quantachrome Quadraorb automatic volumetric instrument. Before the gas adsorption measurements, activation of the sample was done at room temperature (for 24 h) followed by 100 ºC (for 36 h) under ultrahigh vacuum (10-8 mbar) for overnight. Thermogravimetric analysis was carried out in TA instrument (SDT Q600) under N 2 atmosphere with a temperature ramp of 10 o C/min from room temperature to 900 o C. H-T-Ac and PVA-Ac polymer gels for the TGA analysis were prepared by adding 30 % weight of H 3 PO 4 in the total weight of the monomer in case of H-T-Ac and PVA in case of PVA-Ac. Figure S1: 13 C NMR spectrum of HEMA-TMPA polymer Figure S2: a) Tensile stress strain plot of H-T-Ac-60% and b) TGA profiles recorded under N 2 atmosphere. S-5

6 Figure S3: Comparative Nyquist plots of a) H-Ac-60% and H-T-Ac-60%, b) H-T-Ac containing varied acid content and c) PVA-Ac-50% and H-T-Ac-50%. The corresponding conductivity values calculated are plotted in the bottom figures (d, e and f). Figure S4: (a) SEM image and (b) EDX mapping of the carbon (YP-80F) used to fabricate the electrode for the supercapacitors. S-6

7 Figure S5: a) N 2 -adosption isotherm of the carbon (YP-80F) used for preparing the electrode for the supercapacitor. Figure S6: EDX mapping of the carbon sample after the in-situ polymerization: a) carbon portion which is taken after the polymerization from the device; b-d) elemental mapping of carbon (b), phosphorus (c) and oxygen (d) which are corresponding to the area represented in a). The thickness of the blank grafoil sheet is found to be around 0.22 mm. After the coating of the active material, the thicknesses of the electrodes with the mass loading of 1.9, 3.3 and 5.7 mg/cm 2 were measured to be 0.29, 0.31 and 0.34 mm, respectively. The total S-7

8 device thicknesses with the polymer gel electrolyte, separator and electrodes were found to be 0.81, 0.88 and 0.92 mm, respectively. Figure S7: Comparative CV profiles of H-T-Ac-S, H-T-Ac-L, and PVA-Ac-S with varied carbon mass loading of a) 1.9, b) 3.3 and c) 5.7 mg/cm 2. Figure S8: Change in capacitance as a function of the current density of a) H-T-Ac-L and b) H-T-Ac-S. CV profiles recorded at 50 mv/s of c) H-T-Ac-L and d) H-T-Ac-S with varied carbon loading. The energy density of H-T-Ac-L, H-T-Ac-S and PVA-Ac-S is 4.8, 4.5 and is 3.1 Wh/Kg respectively at a current density of 1 ma/cm 2. At the same current density, corresponding power density is 55.8 W/Kg for H-T-Ac-L, 57.5 W/Kg for H-T-Ac-S and 57.5 W/kg for PVA-Ac-S. S-8

9 Figure S9: a) Comparative CV profiles recorded at 50 mv/s in various electrolytes; b) Nyquist plot of the YP-80F carbon measured in 0.5 M H 2 SO 4 as the electrolyte. Chargedischarge profiles of the device taken at the current densities of c) 1 ma/cm 2 and d) 10 ma/cm 2 by using 0.5 M H 2 SO 4 as the electrolyte. Figure S10: a) CV profile taken at 50 mv/s and b) charge-discharge profile recorded for the YP-80F carbon at a current density of 2 ma/cm 2 in 1 M TEABF 4 /propylene carbonate. S-9

10 Figure S11: a) Mass specific capacitance, b) areal capacitance and c) volumetric capacitance values of the various devices with varied electrode mass loading. Capacitance is calculated at a current density of 20 ma/cm 2. Figure S12: Comparative Nyquist plots of the devices with varied electrode mass loadings, a) 1.9 mg/cm 2, b) 3.3 mg/cm 2 and c) 5.7 mg/cm 2 S-10

11 Figure S13: Cycling stability study of the H-T-Ac-S devices with the electrode mass loading of a) 1.9 b) 3.3 and c) 5.7 mg/cm 2. The cycling stability test was carried out by the chargedischarge method at a current density of 5 ma/cm 2. S-11

12 Figure S14: Image of a gel electrolyte carbon mixture prepared through in situ polymerization. Figure S15: Fitted Nyquist plots from the EIS study of the flexible H-T-Ac-S device of 12 cm 2 area having an electrode mass loading of 7.3 mg/cm 2 ; the measurements where carried out before and after the charge-discharge stability cycling. Reference (1) Chen, W.; Fan, Z.; Gu, L.; Bao, X.; Wang, C. Enhanced Capacitance of Manganese Oxide via Confinement Inside Carbon Nanotubes Chem. Commun., 2010, 46, S-12