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Abstract: Carbon-coated lithium iron phosphate (LiFePO4/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12wt%. The use of the modified MA process to synthesize LiFePO4/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density. [Copyright &y& Elsevier]

Abstract: Carbon-coated LiFePO4 (LiFePO4/C) composite cathode-active materials of submicron size and phase-pure olivine structure were synthesized by a mechanical activation (MA) process. The conductive carbon coating was achieved by addition of (i) carbon powder directly or (ii) sucrose as the carbon precursor, during synthesis. LiFePO4/C containing 6wt% carbon prepared by the two methods showed good electrochemical properties as cathodes in lithium batteries at room temperature with high active material utilization of >94% at 0.1C rate and stable cycle performance. The sucrose precursor method leads to the formation of a thin, porous and more uniform carbon coating around the particles and results in a slightly higher discharge capacity (∼3%) compared to the other sample. [Copyright &y& Elsevier]

Abstract: Pure, nano-sized LiFePO4 and carbon-coated LiFePO4 (LiFePO4/C) positive electrode (cathode) materials are synthesized by a mechanical activation process that consists of high-energy ball milling and firing steps. The influence of the processing parameters such as firing temperature, firing time and ball-milling time on the structure, particle size, morphology and electrochemical performance of the active material is investigated. An increase in firing temperature causes a pronounced growth in particle size, especially above 600°C. A firing time longer than 10h at 600°C results in particle agglomeration; whereas, a ball milling time longer than 15h does not further reduce the particle size. The electrochemical properties also vary considerably depending on these parameters and the highest initial discharge capacity is obtained with a LiFePO4/C sample prepared by ball milling for 15h and firing for 10h at 600°C. Comparison of the cyclic voltammograms of LiFePO4 and LiFePO4/C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO4/C in lithium batteries cycled at room temperature. At the high current density of 2C, an initial discharge capacity of 125mAhg−1 (73.5% of theoretical capacity) is obtained with a low capacity fading of 0.18% per cycle over 55 cycles. [Copyright &y& Elsevier]

Abstract: The phospho-olivines LiMPO4 (where M denotes Fe, Mn, Co, Ni) have attracted a lot of attention in recent years as potential positive electrode materials for lithium batteries. The solid–solution Li(Mn y Fe1− y )PO4 has been particularly promising since it operates at the desirable cell voltage of 3.4–4.1V vs. Li+/Li. In this work, Li(Mn0.4Fe0.6)PO4 synthesized by a modified mechanical activation method was evaluated for electrochemical performance as the cathode material in lithium metal battery at room temperature. Phase-pure particles of size ∼100nm were prepared with a conductive, thin web of carbon surrounding them, by incorporating carbon powder as additive during the synthesis. Cyclic voltammetry showed the active voltage range of the material which consists of two pairs of redox peaks: 3.47V corresponding to Fe3+/Fe2+ reaction and 4.02V corresponding to Mn3+/Mn2+ reaction. An initial discharge capacity of 139mAh/g and a stable cycling property were attained at 0.1 C-rate, attributed to the small particle size and the effective conductive coating achieved for the material by the efficient synthesis process. [Copyright &y& Elsevier]

Abstract: An efficient synthesis based on mechanical activation (MA) was developed for carbon-coated lithium iron phosphate (LiFePO4/C). The conventional MA process was modified by introducing two initial steps of slurry phase blending of the ingredients and solvent removal by rotary evaporation, so as to get an intimate mixing and homogenous dispersion of conductive carbon in the sample. Phase-pure, nanometer-sized particles of the active material covered with a porous, nanometer-sized web of carbon were obtained. LiFePO4/C exhibited remarkably good electrochemical properties when evaluated as cathodes in room temperature lithium cells. An initial discharge capacity of 166 mAh/g (corresponding to 97.6% of theoretical capacity) was achieved at 0.1 C-rate. A very stable cycle performance was also realized; good capacity retention up to 100 cycles was achieved at different current densities. [Copyright &y& Elsevier]

Abstract: Composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} and different composition of silica have been prepared by electrospinning polymer solution containing in situ generated silica. These membranes are made up of fibers of 1–2μm diameters. These fibers are stacked in layers to produce fully interconnected pores that results in high porosity. Polymer electrolytes were prepared by immobilizing 1M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) in the membranes. The composite membranes exhibit a high electrolyte uptake of 550–600%. The optimum electrochemical properties have been observed for the polymer electrolyte containing 6% in situ silica to show ionic conductivity of 8.06mScm−1 at 20°C, electrolyte retention ratio of 0.85, anodic stability up to 4.6V versus Li/Li+, and a good compatibility with lithium metal resulting in low interfacial resistance. A first cycle specific capacity of 170mAhg−1 was obtained when the polymer electrolyte was evaluated in a Li/lithium iron phosphate (LiFePO4) cell at 0.1C-rate at 25°C, corresponding to 100% utilization of the cathode material. The properties of composite membrane prepared with in situ silica were observed to be comparatively better than the one prepared by direct addition of silica. [Copyright &y& Elsevier]

Pt-TiO2 nanocomposite catalysts in different Pt:Ti atomic ratios (1:1, 2:1 and 3:1) were synthesized in acidic (pH < 3) and basic (pH >10) medium for oxygen reduction reaction of proton exchange membrane fuel cells. The pH of synthesis medium significantly affected both physicochemical and catalytic properties of Pt-TiO2. Pt-TiO2 prepared in acidic medium exhibited smaller crystallite size, higher specific surface area and more non-stoichiometric titania with higher electrical conductivity as compared to that prepared in basic medium. The oxygen reduction reaction performance from fuel cell polarization curves showed that, Pt-TiO2 catalysts synthesized in acidic medium performed better than those prepared in basic medium. Among the catalysts with varying Pt:Ti atomic ratios, performance decreased in the order 3:1 > 2:1 > 1:1. Among all, Pt:Ti 3:1-A was found to exhibit better fuel cell performance as ORR catalyst (power density-530 mWcm-2; mass activity-123 mAmg-1Pt) compared to commercial Pt/C catalyst (power density-440 mWcm-2; mass activity-87 mAmg-1Pt), under identical conditions. The favourable conditions of synthesis of Pt-TiO2 catalyst achieved in acidic medium contribute to its enhanced properties.