Manoj Kumar Singh

Synthesis of surfactant-free SnS nanorods by a solvothermal route with better electrochemical properties towards supercapacitor applications

We demonstrate a simple, low cost, and eco-friendly synthesis of surfactant free tin monosulfide (SnS) nanorods by a solvothermal route for applications in supercapacitor devices with high specific capacitance. The as-synthesized SnS nanorods, consisting of an intrinsic layered structure, were thoroughly characterised by XRD, TEM, HRTEM, SEM, EDAX and BET techniques to determine their crystal structure, size, morphology and surface area. To explore potential applications for supercapacitors, the nanocrystals were used to fabricate a two electrode system without adding any binder, large area support or conductive filler, and the system was characterised by cyclic voltammograms, galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements in aqueous 2 M Na2SO4 electrolyte. These SnS nanorods exhibit enhanced supercapacitor performance with specific capacitance, energy density and power density values of ∼70 F g−1, 1.49 W h kg−1 and 248.33 W kg−1, respectively, which are found to be two times higher than those of SnS–carbon composites, and thus make SnS nanorods a better alternative source for energy storage devices.

Development of SnS2/RGO nanosheet composite for cost-effective aqueous hybrid supercapacitors

The development of low cost supercapacitor cells with unique capacitive properties is essential for many domestic and industrial purposes. Here we report the first ever application of SnS2-reduced graphene oxide (SnS2/RGO) layered nanocomposite as a superior electrode material for symmetric aqueous hybrid supercapacitors. We synthesized SnS2/RGO nanocomposite comprised of nanosheets of SnS2 and graphene oxide via a one-pot hydrothermal approach. in situ as-synthesized SnS2/RGO is devised for the first time to give high specific capacitance 500 Fg-1, energy density 16.67 Wh kg-1 and power density 488 W kg-1. The cell retains 95% charge/discharge cycle stability up to 1000 cycles. In-short, the SnS2/RGO nanosheet composite presented is a novel and advanced material for application in high stability moderate value hybrid supercapacitors. All the currently available surveys in literature state the potential applicability of SnS2 as the anode material for reversible lithium/sodium ion batteries (LIBs/NIBs) but there is a lack of equivalent studies on electrochemical capacitors. We filled up this knowledge gap by the use of the same material in a cost-effective, highly active hybrid supercapacitor application by utilizing its pseudocapacitance property combined with the layered capacitance property of graphene sheets.

‘Bucky gel’ of multiwalled carbon nanotubes as electrodes for high performance, flexible electric double layer capacitors

We report the preparation of a gelled form of multiwalled carbon nanotubes (MWCNTs) with an ionic liquid 1-butyl-1-methyl pyrrolidinium bis(trifluoromethane sulfonyl)imide (BMPTFSI)), referred to as bucky gel, to be used as binderless electrodes in electrical double layer capacitors (EDLCs). The characteristics of gelled MWCNTs are compared with pristine MWCNTs using transmission electron microscopy, x-ray diffraction and Raman studies. A gel polymer electrolyte film consisting of a blend of poly(vinylidene fluoride-co-hexafluoropropylene) and BMPTFSI, exhibiting a room temperature ionic conductivity of 1.5 × 10(-3) S cm(-1), shows its suitability as an electrolyte/separator in flexible EDLCs. The performance of EDLCs, assembled with bucky gel electrodes, using impedance spectroscopy, cyclic voltammetry and charge-discharge analyses, are compared with those fabricated with pristine MWCNT-electrodes. An improvement in specific capacitance (from 19.6 to 51.3 F g(-1)) is noted when pristine MWCNTs are replaced by gelled MWCNT-binderless electrodes. Although the rate performance of the EDLCs with gelled MWCNT-electrodes is reduced, the pulse power of the device is sufficiently high (~10.5 kW kg(-1)). The gelled electrodes offer improvements in energy and power densities from 2.8 to 8.0 Wh kg(-1) and 2.0 to 4.7 kW kg(-1), respectively. Studies indicate that the gel formation of MWCNTs with ionic liquid is an excellent route to obtain high-performance EDLCs.

Ionic liquid-based sodium ion-conducting composite gel polymer electrolytes: effect of active and passive fillers

We report the studies on composite gel polymer electrolytes (GPEs) comprising 0.5xa0M solution of sodium trifluoromethane sulfonate (Na-triflate or NaTf) in ionic liquid 1-ethyl 3-methyl imidazolium trifluoromethane sulfonate (EMITf) entrapped in poly (vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP) dispersed with passive filler Al2O3 and active filler NaAlO2 particles. The free-standing films of the composite GPEs, prepared from solution-cast method, offer optimum ionic conductivity at room temperature (6.3–6.8u2009×u200910−3xa0Sxa0cm−1 and 5.5–6.5u2009×u200910−3xa0Sxa0cm−1 for Al2O3- and NaAlO2-dispersed GPEs, respectively), with sufficient electrochemical stability and excellent thermal stability up to 340xa0°C. As observed from XRD and SEM, the composites are of predominantly amorphous and porous character, which support the high ionic conduction. The sodium ion transport number has been found to be ∼0.27 for Al2O3-dispersed GPE and 0.42 for NaAlO2-dispersed GPE, which indicates the predominant role of passive and active fillers, Al2O3 and NaAlO2, respectively. The dispersion of NaAlO2 enhances the sodium ion conductivity in composite GPE substantially. The overall ionic conductivity is same as in the case of Al2O3 dispersion. The performance characteristics of GPE, particularly, dispersed with active filler NaAlO2 show its potential applicability as electrolyte/separator in sodium batteries.

Performance of solid-state hybrid supercapacitor with LiFePO4/AC composite cathode and Li4Ti5O12 as anode

We report the studies on quasi-solid battery-supercapacitor (BatCap) systems fabricated using sol–gel-prepared LiFePO4 and its composites (LACs) with activated charcoal (AC) as hybrid cathode and Li4Ti5O12 powder as anode separator by flexible gel polymer electrolyte (GPE) film. The GPE film comprises 1.0xa0M lithium trifluoromethane sulfonate (LiTf) solution in ethylene carbonate (EC)–propylene carbonate (PC) mixture, immobilized poly(vinylidene fluoride-co-hexafluoro-propylene) (PVdF-HFP), which is of high ionic conductivity (∼3.8xa0×xa010−3xa0Sxa0cm−1 at 25xa0°C) and electrochemical stability window (∼3xa0V). The effect of the addition of AC in composite electrode LACs has been analyzed using various techniques such as X-ray diffraction, porosity analysis, and electrochemical methods. The interfaces of composite LACs and GPE film not only offer high rate performance but also show high specific energy (>27.8xa0Whxa0kg−1) as compared to the symmetric supercapacitors and pristine lithium iron phosphate (LiFePO4)-based lithium ion batteries. The full BatCap systems have been characterized by cyclic voltammetry and galvanostatic charge–discharge tests. The BatCap systems with composite electrodes (LACs) offer better cyclic performance as compared to that of pristine LiFePO4-based BatCap or LIB LiFePO4/Li4Ti5O12.

A free-standing, flexible PEDOT:PSS film and its nanocomposites with graphene nanoplatelets as electrodes for quasi-solid-state supercapacitors

Research and development on all-solid-state, flexible supercapacitors is the prime concern of the scientific community these days due to their various advantages including their easy transportability, miniaturization, and compactness in different appliances. We report the novel configuration of all-solid symmetrical supercapacitors employing free-standing, flexible films of poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and its nanocomposite electrodes with graphene nanoplatelets (GNPs), separated by ionic liquid (IL) (1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMITf))-based gel polymer electrolyte (GPE) films. The free-standing and flexible form of PEDOT:PSS/GNP nanocomposite films have been prepared via simple mixing of the two counterparts. Scanning electron microscopy, x-ray diffraction, Raman analysis, and thermal and mechanical characterizations have been performed to ascertain the suitability of pristine and nanocomposite PEDOT:PSS films as potential supercapacitor electrodes. The GPE film, comprising of a solution of NH4CF3SO3 (NH4-triflate or NH4Tf) in IL, entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), is a promising electrolyte due to its high ionic conductivity and sufficient electrochemical stability window. The supercapacitor with a PEDOT:PSS nanocomposite containing ∼3.8 wt.% of GNP has been found to give an optimum specific capacitance of ∼106 F g-1 (evaluated from electrochemical impedance spectroscopy), and specific energy and power of ∼6.95 Wh kg-1 and 2.58 kW kg-1, respectively (evaluated from galvanostatic charge-discharge). More importantly, the capacitors demonstrate stable performance for more than 2000 charge-discharge cycles, with only ∼10% initial fading in capacitance. Interestingly, the PEDOT:PSS/GNP nanocomposite-based solid-state supercapacitors with the IL-incorporated GPE have shown comparable (even better) performance than other reported PEDOT:PSS-based supercapacitors.