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M V Reddy1 A Shahul2 Chua Chattrapat1 Stefan Adams1

1, National University of Singapore, Singapore, , Singapore
2, Qatar University, Doha, , Qatar

Conventional positive (cathodes) electrode materials for lithium-ion 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 synthesis of materials suitable for alternative electrode concepts including transition metal fluorides that operate by a conversion type mechanism (1) and a promising new type of alternative nanocomposite composite cathodes, where the storage of lithium and of charge is distributed over two components of a nanocomposite containing LiF and or metal oxides, MO (M= Mn, Fe, Co, Ni, Cu) (2,3).
Transition metal fluorides MF2 (M=Fe, Mn, Zn) were derived from one dimensional metal organic frameworks (MOF) by a polymer (PVDF) assisted decomposition 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 (PVDF) and the eventual decomposition lead to carbon coated metal fluoride nanoparticles of high surface area of >200 m2/g. 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) and preliminary galvanostic cycling of FeF2 demonstrates that the material exhibit stable and good reversible capacity of 580 mAh/g during the initial cycles and slight capacity fading has been observed after 20 cycles. Further optimization of the performance is being carried out. Whereas MnF2 and ZnF2 showed reversible capacity of 220 and 200 mAh/g and retained a capacity around 100 mAh/g after 20 cycles.
Nanocomposites of divalent transition metal oxides MO (M= Mn, Fe, Co, Ni, Cu) and LiF were prepared ball-milling method. The obtained materials will be characterized in detail by X-ray diffraction; Scanning and Transmission electron microscope (SEM/TEM) are used study the morphology. Raman, X-ray photoelectron spectroscopy are used understand structure, vibrational bands and oxidation state of the materials and BET surface area method. Structural and microstructural variations during charge-discharge cycling were characterized by in operando X-ray diffraction for elected promising compositions. Electrochemical properties will be evaluated voltage, range 4 to 1.0 vs. Li in the voltage using cyclic voltammetry at scan rate of 0.075 mV/sec, galvanostatic cycling at a current rate of 0.1C, and electrochemical impedance spectroscopy. Preliminary electrochemical studies yield a reversible capacity of 100 mAh/g. Further long term cycling studies of the nanocomposites are in progress.

References
(1) Cabana, J etal. .; . Adv. Mater. 2010, 22, E170.
(2) Jung, S.-K.; etal. Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries. 2017, 2, 16208.
(3) Poizot, P. etal Nano-sized transition-metaloxides as negative-electrode materials for lithium-ion batteries. Nature 2000, 407, 496.

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