Faculty Publications
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Item LiClO4-doped plasticized chitosan as biodegradable polymer gel electrolyte for supercapacitors(2009) Muthu, M.S.; Bhat, D.K.Studies on redox supercapacitors using electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In this study, electrochemical properties of a chitosan-based biodegradable polymer gel electrolyte (PGE) and a p/p polypyrrole supercapacitor fabricated using this electrolyte have been investigated. The variation of conductivity and dielectric properties of the electrolyte film with temperature has also been measured. The PGE film chosen for the study exhibited a specific conductivity of 5.5 × 10-3 S cm~. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The fabricated supercapacitor showed a fairly good specific capacitance of 120 F g-1 and a time constant of 1 s. © 2009 Wiley Periodicals, Inc.Item LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors(Institute for Ionics, 2013) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.Biodegradable polymer electrolyte comprising the blend of chitosan (CS) and poly(ethylene glycol) (PEG) plasticized with ethylene carbonate and propylene carbonate, as host polymer, and lithium perchlorate (LiClO4), as a dopant, was prepared by solution casting technique. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. The variation of conductivity and dielectric properties has been investigated as a function of polymer blend ratio, plasticizer content and LiClO4 concentration at temperature range of 298-343 K. The DSC thermograms show two broad peaks for CS/PEG blend and increased with increase in the LiClO4 content. The maximum conductivity has been found to be 1. 1 × 10-4 S cm-1 at room temperature for 70:30 (CS/PEG) concentration. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The activation energy of all samples was calculated using the Arrhenius plot, and it has been found to be 0. 12 to 0. 38 eV. A carbon-carbon supercapacitor has been fabricated using this electrolyte, and its electrochemical characteristics and performance have been studied. The supercapacitor showed a fairly good specific capacitance of 47 F g-1. © 2012 Springer-Verlag.Item Tubular array, dielectric, conductivity and electrochemical properties of biodegradable gel polymer electrolyte(Elsevier Ltd, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.A supercapacitor based on a biodegradable gel polymer electrolyte (GPE) has been fabricated using guar gum (GG) as the polymer matrix, LiClO4 as the doping salt and glycerol as the plasticizer. The scanning electron microscopy (SEM) images of the gel polymer showed an unusual tubular array type surface morphology. FTIR, DSC and TGA results of the GPE indicated good interaction between the components used. Highest ionic conductivity and lowest activation energy values were 2.2 × 10-3 S cm-1 and 0.18 eV, respectively. Dielectric studies revealed ionic behavior and good capacitance with varying frequency of the GPE system. The fabricated supercapacitor showed a maximum specific capacitance value of 186 F g -1 using cyclic voltammetry. Variation of temperature from 273 K to 293 K did not significantly influence the capacitance values obtained from AC impedance studies. Galvanostatic charge-discharge study of supercapacitor indicated that the device has good stability, high energy density and power density. © 2013 Elsevier Ltd. All rights reserved.Item Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor(Royal Society of Chemistry, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.; Senthil Kumar, S.Graphite extracted from a used primary cell was converted into reduced graphene oxide (rGO) using calcium carbonate together with rapid and local Joule heating by microwave irradiation. Electrodes were prepared by ultrasonically dispersing rGO in biodegradable poly(vinylpyrrolidone) (PVP) binder and coating this on recyclable poly(ethyleneterephthalate) (PET) sheet using a low cost screen printing technique. The use of the same polymer (PVP) as a binder, in addition to as the solid polymer electrolyte (SPE), enhances the compatibility and ionic conductivity of the hydrophobic rGO electrode in the supercapacitor system. Further, the phosphoric acid (H3PO4)-doped biodegradable SPE was screen printed for the first time on the rGO electrodes. Ionic conductivity and dielectric studies of the SPE were carried out at different temperatures and different dopant acid concentrations. The morphology, composition and structure of the graphene electrode components were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. Transmission electron microscopy (TEM) images showed a single layer or a few layers of rGO sheets and selected area electron diffraction showed the presence of slight defects. The fabricated environmentally friendly, industrially favorable and green supercapacitor showed a specific capacitance of 201 F g-1 and cyclic stability with 97% retention of the initial capacitance over 2000 cycles. Furthermore, the performance of this green supercapacitor is comparable to that of those fabricated using rGO synthesized from commercial graphite and in other literature reports. © 2014 The Royal Society of Chemistry.Item Effect of acid dopants in biodegradable gel polymer electrolyte and the performance in an electrochemical double layer capacitor(Institute of Physics Publishing custserv@iop.org, 2015) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.Proton-conducting biodegradable gellan gum gel polymer electrolytes (GPEs) have been prepared using three different dopants, namely ortho-phosphoric (o-H3PO4), sulfuric (H2SO4) and hydrochloric acids (HCl). The GPEs were cross-linked using borax. The polymeric gels were characterized by spectroscopic, thermal, ionic conductivities and dielectric measurements. Proton conductivity was in the range of 5.1 × 10-3 to 3.7 × 10-4 s cm-1 and activation energies were between 0.14 meV and 0.19 meV, at different temperatures. Among the doped acids, the H3PO4 doped GPE exhibited thermal stability at varying temperature. Electrochemical double layer capacitors (EDLCs) were fabricated using activated carbon as electrode material and GPEs. The EDLCs were tested using cyclic voltammetry, ac impedance spectroscopic and galvanostatic charge-discharge techniques. The maximum specific capacitance value was 146 F g-1 at a scan rate of 2 mV s-1. Quite stable values were obtained at a constant current density up to 1000 cycles. © 2015 The Royal Swedish Academy of Sciences.Item Preparation and characterization of phosphoric acid-doped hydroxyethyl cellulose electrolyte for use in supercapacitor(SpringerOpen, 2015) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.A new borax cross-linked biodegradable solid polymer electrolyte based on hydroxyethyl cellulose and phosphoric acid (H3PO4) was prepared. Characterizations of doped and undoped SPE were done using Fourier transform infrared spectroscopic and electrochemical studies. The ionic conductivity of the films increased with increase in acid concentration and the ionic conductivity obtained at 303 K was 4.1 × 10-3 S cm-1. Furthermore, effects of acid concentration on ionic conductivity and activation energy were discussed. Dielectric studies showed long tail-like feature indicating capacitive nature. A supercapacitor was fabricated and its electrochemical characteristics were studied. The supercapacitor showed a fairly good specific capacitance of 83 F g-1 at 2 mV s-1 and galvanostatic charge-discharge studies showed the mirror-like pattern with 98 % columbic efficiency. Cyclic stability was measured up to 2000 cycles. © 2015 The Author(s).Item A new strategy of PVDF based Li-salt polymer electrolyte through electrospinning for lithium battery application(Institute of Physics Publishing helen.craven@iop.org, 2019) Janakiraman, S.; Surendran, A.; Ghosh, S.; Anandhan, S.; Adyam, A.Polyvinylidene fluoride (PVDF) ultrafine fibers with different proportions of lithium nitrate (LiNO3) were fabricated by an electrospinning device. The processing parameters are optimized to 19 wt% PVDF to get a bead free structure. Scanning electron microscope (SEM) and atomic force microscope (AFM) showed the uniform and interconnected porous structure. With the addition of 2 wt% LiNO3, the fiber diameter of the electrospun membrane decreased from 371 to 222 nm. Furthermore, the addition of LiNO3 into the nanofibrous membrane enhanced the ionic conductivity from 0.97 ×10-3 S cm-1 to 1.61 ×10-3 S cm-1 at room temperature after soaking with 1 M LiPF6 (lithium hexafluoro-phosphate) in ethylene carbonate (EC) and diethyl carbonate (DEC) in (1:1 wt%). Compared with the conventional Celgard and pristine PVDF membrane, the salt doped PVDF membranes showed higher electrochemical stability window and lower interfacial resistance. The electrospun membrane separators (ES) were assembled into Lithium cobalt oxide (LiCoO2) as cathode and lithium metal as an anode. The salt doped membrane showed superior discharge, C-rate and stable cycle performance than the commercial Celgard membrane. © 2018 IOP Publishing Ltd.Item Electrospun electroactive polyvinylidene fluoride-based fibrous polymer electrolyte for sodium ion batteries(Institute of Physics Publishing helen.craven@iop.org, 2019) Janakiraman, S.; Surendran, A.; Biswal, R.; Ghosh, S.; Anandhan, S.; Adyam, A.Electrospinning is an efficient technique to produce ultrafine electroactive mat, diameters ranging from few nanometers to micrometers to use as a separator in sodium ion battery. The polyvinylidene fluoride (PVDF) polymer solution was optimized to 19 wt%, applied voltage 25 kV and flow rate of 0.5 ml h-1 to get a bead free ultrafine electroactive structure. The electroactive ?-phase is confirmed by x-ray diffractometer (XRD). Ionic conductivities, electrolyte uptake, wettability, linear sweep voltammetry (LSV) and thermal stability of the electroactive fibrous polymer electrolyte (EFPE) were studied by soaking the separator with a liquid electrolyte of 1 M sodium hexafluorophosphate (NaPF6) dissolved in ethylene carbonate (EC)/propylene carbonate (PC) (1:1 vol%). The EFPE exhibits high ionic conductivity of 1.08 mS cm-1 and electrochemical stability window of 5.0 V versus Na/Na+ under ambient condition. The half-cell containing Na0.66Fe0.5Mn0.5O2 as cathode and EFPE as the separator cum electrolyte showed a stable cycling performance at a current rate of 0.1C. © 2019 IOP Publishing Ltd.Item PVDF/halloysite nanocomposite-based non-wovens as gel polymer electrolyte for high safety lithium ion battery(John Wiley and Sons Inc. cs-journals@wiley.com, 2019) Khalifa, M.; Janakiraman, S.; Ghosh, S.; Adyam, A.; Anandhan, S.Gel polymer electrolyte (GPE) based on electrospun poly(vinylidene fluoride) (PVDF)/halloysite nanotube (HNT) nanocomposite non-wovens was synthesized and its suitability as a separator in lithium-ion battery (LIB) was explored. In this study, HNT played a key role in reducing the average diameter of the electrospun fibers and uplifted the porosity of the non-wovens thereby improving their electrolyte uptake. Due to a reduction in crystallinity and increased % porosity of the PVDF/HNT non-wovens, the ionic conductivity (1.77 mScm?1) and ionic transport across the separator were improved. Moreover, this GPE separator exhibited high tensile and puncture strength with negligible thermal shrinkage and a higher melting temperature compared with a commercially available separator, which is vital from the safety perspective. The cycling performance of Li/GPE/LiCoO2 cell was evaluated and it exhibited a high capacity of 138.01 mAhg?1 with 97% coulombic efficiency for the initial cycle. The cell was stable and retained its high performance with little loss in capacity even after repeated charge–discharge cycles. Such a combination of high ionic conductivity, tensile strength with low thermal shrinkage is seen to be very rare in polymer-based separators. It is noteworthy that this novel GPE outperformed the commercial separator also in the cycle performance. POLYM. COMPOS., 40:2320–2334, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics EngineersItem An electroactive ?-phase polyvinylidene fluoride as gel polymer electrolyte for magnesium–ion battery application(Elsevier B.V., 2019) Singh, R.; Janakiraman, S.; Khalifa, M.; Anandhan, S.; Ghosh, S.; Adyam, A.; Biswas, K.The gel polymer electrolytes (GPEs) are currently interesting research area in rechargeable batteries. In the present study, synthesis and characterization of electroactive gel polymer electrolyte (EGPE) for Mg-ion batteries application have been investigated. The bead free electroactive polyvinylidene fluoride (PVDF) with high porosity is achieved by an electrospinning process. The ?-phase of PVDF is polar and electroactive with a high dipole moment. Electroactive ?-phase is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscopy (FESEM) study is done to analyze the structure and morphology of the electroactive membrane. The electroactive gel polymer electrolyte is formed by immersing an electroactive PVDF membrane in 0.3 M magnesium perchlorate (MgClO4) and propylene carbonate (PC) solution. The ionic conductivity of electroactive ?-phase PVDF membrane is achieved to be 1.49 mS cm?1 at 30 °C, which is higher than commercial available polypropylene (PP) Celgard. Tortuosity of electroactive gel polymer electrolyte is found to be 1.44. The voltage stability of the EGPE is stable up to a high voltage of 5.0 V against Mg+2/Mg. The total ionic transference number and magnesium ion transference number of EGPE are also investigated to confirm high ionic conductivity. © 2019 Elsevier B.V.