Conventional positive (cathodes) electrode materials for lithium batteries, use mixed-conducting lithium containing transition metal oxides, metal phosphates etc. which are able to store both lithium and electrons by changing their oxidation state. In this presentation, we discuss the facile synthesis of materials suitable for alternative electrode concepts including Transition metal fluorides MF2 (M=Fe, Mn, Zn) were obtained by reacting Fe, Mn, Zn-Metal salts with fumaric acid as a one-dimensional metal organic framework, and a polymer (PVDF) as Fluorine source, final products are obtained by heating at 600°C, 6h in Ar gas. The MOF were initially prepared by a simple chimie douce method. Incorporation of the MOF with a fluorinated polymer and the eventual decomposition lead to carbon coated metal fluoride nanoparticles of high surface area of >200 m2/g for FeF2. The obtained materials will be characterized in detail by X-ray diffraction, Scanning and Transmission electron microscope (SEM/TEM) are used to evaluate the structure and morphology, X-ray photoelectron spectroscopy are used understand structure, vibrational bands and oxidation state of the materials and BET surface area method. Electrochemical studies were carried out in the voltage, range 4 to 1.0 vs. Li, at current rate of 50 mA/g (0.1 C) using 1MLiPF6 (EC;DEC) as liquid electrolyte and tested with Li-metal as a counter and reference electrodes. The cyclic voltammetry at scan rate of 0.075 mV/sec at room temperature (24°C). Galvanostatic cycling of FeF2 demonstrates that the material exhibit stable and good reversible capacity of 580 mAh/g during the first cycle and slight capacity fading has been observed after 20 cycles. Further studies on rate performance is being carried up to 2.5 C rate. Whereas MnF2 and ZnF2 showed reversible capacity of 220 and 200 mAh/g and retained a capacity around 100 mAh/g after 20 cycles and showed lower capacity than FeF2. Discuss the structural, reaction mechanism of FeF2 during charge-discharge cycling by in situ/operando X-ray diffraction and electrochemical impedance spectroscopy studies discuss in detail. Keywords: Metal fluorides (MF2 M=Fe, Zn, Mn); Electrochemical properties; Insitu studies; Electrochemical impedance spectroscopy; energy storage
Commercial lithium ion batteries (LIBs) use layer-type compounds, lithium cobalt oxide (LiCoO2) or LiFePO4 as the cathode (positive electrode) and graphite (C) as the anode (negative electrode) material, and a non-aqueous Li- ion conducting electrolyte. The liquid electrolyte in the form of a solution or immobilized in a gel-polymer. LIBs with an operating voltage of 3.6 V are extensively used in the present-day portable electronic devices like, cell phones and other low power operated devices. For high-power applications like, electric/hybrid electric vehicles and back-up power supplies and, the LIBs need to satisfy several criteria, namely, cost-reduction, improvement in the energy density, safety-in-operation at high current charge/discharge rates and improvement in the low-temperature-operation. To satisfy the above criteria, researches are being carried out worldwide to find alternative cathode materials. In my presentation, I will discuss our group studies on V-based Flouro phosphates cathode materials. Specifically, I will focus bare and Fe doped-LiVPO4F, αI-LiVOPO4 and V-based metal organic framework materials, MX[(VO)2N2(C2O4)], where M= K, Li, Na , N= HPO4, HPO3. and LiSiV2O6. Materials were prepared variety of chemical methods carbothermal/Graphenothermal reduction, hot plate and hydrothermal methods. Materials were characterized by Rietveld refinement X-ray diffraction, X-ray photoelectron spectroscopy, Raman, XPS, Microscopy (SEM &TEM) and BET surface area methods. Electro analytical studies like cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy techniques. Interestingly V-based cathodes showed around 4 V redox couple (except LiSiV2O6) which is higher than that of LiFePO4 (3.5V vs. Li) and observed reversible capacity is order 80-140 mAh/g. Discuss in detail long term cycling studies and rate capabilities and reaction mechanisms. Keywords: Materials synthesis; Batteries; Cathodes; Electrochemical Properties; Energy storage References 1. M.V. Reddy, M. V.; G.V. Subba Rao, B.V.R. Chowdari, Chem. Rev. 113 (2013) 5364 2. A.S. Hameed, M.V. Reddy*, M. Nagarathinam, T. Runčevski, R.E. Dinnebier, S. Adams, B.V.R. Chowdari, J.J. Vittal, Scientific Reports, 5 (2015) 16270 3. M. Shahul, M. V. Reddy*, N.Sarakar, B. V. R. Chowdari,J. J. Vittal RSC Adv., 5(2015), 60630 4. M. Shahul, M. Nagarathinam, M. V. Reddy*, B. V. R. Chowdari,J. J. Vittal Journal of Materials Chemistry 22(2012)7206-7213. 5. M. Nagarathinam, K. Saravanan, E. J. Han Phua, M. V. Reddy*, B. V. R. Chowdari,J. J. Vittal Angewandte Chemie Intl. 51(24)(2012)5866-5870. 6. M .V. Reddy, G.V. Subba Rao and B. V. R. Chowdari Journal of Power Sources 195(2010)5768-5774.
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