Varun Kumar Singh

Development of ion conducting polymer gel electrolyte membranes based on polymer PVdF-HFP, BMIMTFSI ionic liquid and the Li-salt with improved electrical, thermal and structural properties

Ion conducting polymer gel electrolyte membranes based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI with and without the Li-salt (having the same anion i.e. the TFSI− anion) have been synthesized. Prepared membranes have been characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR), differential scanning calorimetry, thermogravimetric analysis (TGA) and complex impedance spectroscopic techniques. Incorporation of IL in the polymer PVdF-HFP/polymer electrolyte (i.e. PVdF-HFP + 20 wt% LiTFSI) changes different physicochemical properties such as melting temperature (Tm), glass transition temperature (Tg), thermal stability, degree of crystallinity (Xc), and ionic transport behaviour of these materials. The ionic conductivity of polymeric gel electrolyte membranes has been found to increase with increasing concentration of IL and attains a maximum value of 2 × 10−3 S cm−1 at 30 °C and ∼3 × 10−2 S cm−1 at 130 °C. A high total ionic transference number >0.99 and the cationic transference number (tLi+) ∼ 0.22 with a wider electrochemical window (ECW) ∼ 4.0–5.0 V for the polymer gel electrolyte membrane containing higher loading of IL (∼70 wt% of IL) have been obtained. Temperature dependent ionic conductivity obeys Arrhenius type thermally activated behaviour.

Development of ionic liquid mediated novel polymer electrolyte membranes for application in Na-ion batteries

Polymer electrolyte membranes based on polymer PEO, ionic liquid, 1-butyl-3-methylimidazolium methylsulfate, BMIM-MS, and salt, sodium methylsulfate, NaMS, {PEO + x wt% BMIM-MS for x = 0 and 20 and (PEO + 10 wt% of NaMS) + x wt% BMIM-MS for x = 0, 20 and 60} were prepared and characterized by various experimental techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA)/differential thermogravimetric analysis (DTGA), differential scanning calorimetry (DSC), ac impedance spectroscopy and cyclic voltammetry (CV). The synthesized polymer electrolyte membranes were free-standing and flexible with good mechanical stability. A Fourier transform infrared spectroscopic (FTIR) study showed the complexation of ether oxygen of the PEO backbone with the cations of the Na-salt or IL (BMIM-MS). SEM, XRD and DSC studies show that the crystallinity of the polymer electrolyte membranes decreases on increasing the concentration of IL due to the plasticization effect of the IL. Ionic conductivity of polymer electrolyte membranes was found to increase with the concentration of IL (BMIM-MS) and showed a maximum room temperature (at ∼30 °C) ionic conductivity of ∼1.05 × 10−4 S cm−1 for 60 wt% IL loading. The plasticization effect of the IL enhanced the amorphicity of the polymeric membranes. This optimized composition of polymer electrolyte shows high electrochemical potential window (∼4–5 V), cationic transference number (i.e. tNa+ ∼ 0.46) and also good cycling between ∼2.7 and ∼1.6 V through charging–discharging.

Effect of phosphonium based ionic liquid on structural, electrochemical and thermal behaviour of polymer poly(ethylene oxide) containing salt lithium bis(trifluoromethylsulfonyl)imide

Solid polymer electrolytes (SPEs) using polymer poly(ethylene oxide) (PEO), lithium salt bis(trifluoromethylsulfonyl)imide (LiTFSI) and ionic liquid (IL) trihexyltetradeylphosphonium bis(trifluoromethylsulfonyl)imide have been prepared. These prepared solid polymer electrolyte films have been characterised by using different experimental techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), complex impedance spectroscopy, Fourier transform infrared spectroscopy (FTIR), an electrochemical analyser etc. Changes in crystallinity, melting temperature (Tm), glass transition temperature (Tg), thermal stability and ionic transport behaviour of the prepared polymer electrolyte have been observed when the LiTFSI salt and different concentrations of IL were incorporated in the pristine polymer PEO. Ionic conductivity of the prepared solid polymer electrolyte (PEO + 20 wt% LiTFSI) has been found to increase with increasing IL concentration in polymer electrolytes up to 20 wt% IL. Total ionic transference number >0.99 and cationic transference number ∼0.37 with an electrochemical window of ∼3.34 V has been observed for the optimized solid polymer electrolyte (PEO + 20 wt% LiTFSI + 20 wt% IL). Temperature dependant ionic conductivity obeys Arrhenius type thermally activated behaviour.

Mixed anion effect on the ionic transport behavior, complexation and various physicochemical properties of ionic liquid based polymer gel electrolyte membranes

Li-ion conducting polymer gel electrolyte membranes (PGEMs) containing ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluroborate BMIMBF4, polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP and lithium bis(trifluoromethanesulfonyl)imide LiTFSI salt (having different anion i.e. BF4− and TFSI−) have been synthesized and characterized by various techniques. The results show that the synthesized PGEMs have good free-standing characteristics, good thermal stability (300–400 °C) and also have a wide electrochemical window (ECW) ∼4.0–4.20 V. The conductivity increases with increasing amount of IL, and attains a value of 3.2 × 10−3 S cm−1 at room temperature for the PGEMs containing higher loadings of IL. A high total ionic transference number (∼0.99) and cationic transference number (tLi+ ∼ 0.33) for the PGEMs containing higher loadings of IL have been obtained.

Role of ionic liquid [BMIMPF6] in modifying the crystallization kinetics behavior of the polymer electrolyte PEO-LiClO4

We report on the modification in crystallization kinetics behavior of PEO + 10 wt% LiClO4 polymer electrolyte by the addition of an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). Three techniques have been used for studying crystallization kinetics, viz., (i) isothermal crystallization technique using DSC, (ii) non-isothermal crystallization technique using DSC, and (iii) by monitoring the growth of spherulites with time in the polymer electrolyte films using a polarizing optical microscope (POM). Results from all the three techniques show that the presence of ionic liquid BMIMPF6 suppresses the crystallization rate due to its plasticization effect. Isothermal crystallization data was well described by the Avrami equation, and Avrami exponent n lies in the range of 1 to 2, which signifies 2D crystal growth geometry occurring in these polymer electrolytes under the investigated temperature range. However, the Avrami crystallization rate constant ‘K’ increases exponentially with crystallization temperature and ionic liquid content as well. However, the non-isothermal crystallization kinetics of these polymer electrolytes is discussed in terms of three different models (Jeziornys, Ozawas and Mos method), and it is found that Mos method better explains the non-isothermal crystallization data. In addition, crystalline morphology and spherulite growth were studied by POM, which shows the suppression in crystallization in the presence of ionic liquid, as confirmed by spherulite growth rate (Gs) analysis.

An unprecedented biogenetic-type chemical synthesis of 1(15-->11) abeotaxanes from normal taxanes.

A one-pot chemical process using BF(3).Et(2)O for the synthesis of a new class of 1(15-->11) abeotaxanes from normal taxanes has been developed. The chemical structures of rearranged 1(15-->11) abeotaxane were established by extensive 2D NMR spectroscopic data.