Papers by Author: Subrata Ray

Abstract: Lithium alloying compounds as an anode materials have been a focused for high capacity lithium ion battery due to their highenergy capacity and safety characteristics. Here we report on the preparation of graphite-tin composite by using ball-milling in liquid media. The composite material has been characterized by scanning electron microscope, energy depressive X-ray spectroscopy, X-ray diffraction and Raman spectra. The lithium-ion cell made from graphite-tin composite presented initial discharge capacity of 1065 mAh/g and charge capacity 538 mAh/g, which becomes 528 mAh/g in the second cycle. The composite of graphite-tin with higher capacity compared to pristine graphite is a promising alternative anode material for lithium-ion battery.

Abstract: In the present work, the effect of Li salt i.e. LiClO₄ contained in composite plasticizer (PC+DEC) with three different concentrations on ionic transport and other electrochemical properties of PMMA based gel polymer electrolytes synthesized has been investigated. The electrolytes have been synthesized by solution casting technique by varying the wt (%) of salt and plasticizer. The formation of polymer-salt complexes and their structural characterization have been carried out by FTIR spectroscopic and XRD analyses. The room temperature ionic conductivity of the electrolyte composition 0.6PMMA-0.125(PC+DEC)-0.15LiClO₄ (wt %) has been found to be maximum whose magnitude is 0.40×10^-5 S/cm as determined by ac impedance analysis. The temperature dependent ionic conductivity of electrolyte sample0.6PMMA-0.125(PC+DEC)-0.15LiClO₄ has further been investigated. Thermal analyses of electrolyte samples of all three compositions have also been done.

Abstract: Different types of carbon nanostructure materials have been grown on nano-sized transition metal oxide based catalyst particles by catalytic chemical vapour deposition. The present investigation reveals an important role of melting or surface melting of oxide catalysts for the growth of carbon nanostructure materials. In the reducing environment prevailing during the growth of nanostructures, oxide catalysts are reduced to metals, which may act as a template for the growth of carbon nanostructure materials. Flow rate of acetylene gas is crucial in catalyzing the growth, as high flow rate of acetylene may cover the catalyst particles with a layer of decomposed carbon, rendering the particles incapable of playing the role of catalyst. The size of the catalyst and the extent of melting, determined primarily by the extent of doping, are important in deciding whether the conditions are favourable for the growth of multi walled carbon nanotube, nanofiber or other nanostructures. Smaller particle size and low doping level favour the growth of multi walled carbon nanotube while growth of nanofiber is commonly observed with larger particles and higher doping level. The size (i.e. diameter) of the nanostructures growing around the catalyst is proportional to the particle size of the catalyst.

Abstract: Zinc ferrite (ZnFe2O4) is a commercially important material and has wide applications. We report the synthesis of nanostructured ZnFe2O4 and Fe-doped ZnO nanorods via a low cost, open to atmosphere self catalyzed Chemical Vapor Deposition(CVD) method which uses the Vapor-Liquid-Solid (VLS) Mechanism for growth. A mixture of Zinc Oxide, Graphite and Zinc powder, along with the substrates were put at the closed end of a quartz tube and placed in a preheated furnace. The parameters varied were 1.)molar ratios 2.)types of substrates and 3.)the furnace temperature. The characterization was done using FE-SEM, TEM,and XRD. The growth morphology varies along the temperature gradient in the tube, resulting in the formation of ZnFe2O4 nanoribbons (800-750 0C), nanoellipsoids (700 0C) and nanowires (650 0C). Fe- doped ZnO nanorods have also formed as scattered bundles along with the zinc ferrite nanoribbons. This is the first reported synthesis of nanoribbon morphology of ZnFe2O4 . The effective diameter:width ratio of the morphology and the Zn atomic percentage decreases along the temperature gradient. Optimized parameters were:1.)mild steel substrates, 2.)furnace temperature 800 0C and 3.)1:1:0.05 molar ratio of ZnO:C:Zn in the reaction mixture. When stainless steel and gold sputtered steels were used as substrates there was no growth. This proves that iron from the substrate takes an active part in the reaction and is critical for the growth. The simplicity of the setup, control over growth morphology and cheap reagents used give the method potential commercial applications.

Abstract: Nanosized powders in the system LiMn2−xFexO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) have been synthesized by sol-gel technique using citric acid as chelating agent. The effect of Fe substitution on the structure and surface morphology of spinel LiMn2O4 has been examined by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and Electrochemical characteristics. The materials for all the compositions except x = 0.6 exhibit a phase pure cubic spinel structure as evident from the XRD analyses. Doping with Fe increases the crystallinity in the materials and decreases the average particle size. The surface morphology of the synthesized particles is spherical and polygonal type. Average particle size lies in the range of 60 to 400 nm. Improved capacity retention in rechargeable 4 V Li/LiMn2-xFexO4 cells has been observed when a small amount of manganese in the spinel cathode is replaced with iron. The first discharge capacities of LiMn2−xFexO4 (x = 0.0, 0.1, 0.2, 0.3) in a voltage range of 3 V to 4.3 V decreases as the x increases, however, the cyclic performance improves.

Abstract: Carbon nanotubes (CNTs) have been synthesized by chemical decomposition of acetylene gas at 580°C and 650°C using catalyst of LiNi0.5Co0.5O2. The effect of decomposition temperature on structure of the CNTs is that, CNTs grown at 650°C have lower defects concentration and higher crystallinity as compared to that grown at 580°C. The porous anodized aluminum oxide (AAO) template (as substrate), catalyst particles and the CNTs grown were analyzed by FE-SEM. The pore diameter in the template lies in range of 30 - 80 nm. The CNTs have been analyzed by using Raman spectroscopy and X-ray diffraction techniques. The up-shift in G-band of graphitic sheet and larger full width at half maximum of the peak in the Raman spectra of the CNT in comparison to those observed for graphite are indicative of the structural modification. XRD results also indicate the structural modification in CNT based on the fact that d-value becomes 3.42 Å, which is larger than 3.35 Å for graphite. The tube diameters lie in the range of 12 - 50 nm.