Ethylene diamine tetra-acetic acid (EDTA) was used to prepare spinel LiMn 2 O 4 at 650 °C. The prepared sample by EDTA (E-LiMn 2 O 4 ) is compared with another spinel sample (C-LiMn 2 O 4 ) prepared by citric acid as a common chelating agent at the higher temperature (800 C) adjusted to obtain the same size and shape of the particles as in (E-LiMn 2 O 4 ) sample, as probed by SEM and TEM images. Investigation of both samples by X-ray diffraction showed that both samples have the single phase cubic spinel LiMn 2 O 4 phase with space group Fd-3m. Vibration properties obtained from Raman scattering (RS) and Fourier Transform Infra-Red (FTIR) spectroscopy for both samples are identical with spinel LiMn 2 O 4 structure. 7 Li MAS NMR and XPS spectra show that the amount of Mn 4+ is larger in LiMn 2 O 4 sample prepared by citric acid. LiMn 2 O 4 sample prepared using EDTA as chelating agent has better structural properties, but the improvement of the electrochemical properties is much smaller than the results reported in the literature for lamellar compounds and silicate materials. This is attributed to the features specific to the spinel, which limit both the capacity and cycle ability: dissolution of manganese and Jahn-Teller distortions associated to Mn 3+ ions, that are not modified by the choice of chelating agent.
This work aimed at synthesizing MoO3 and MoO2 by a facile and cost-effective method using extract of orange peel as a biological chelating and reducing agent for ammonium molybdate. Calcination of the precursor in air at 450 °C yielded the stochiometric MoO3 phase, while calcination in vacuum produced the reduced form MoO2 as evidenced by X-ray powder diffraction, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy results. Scanning and transmission electron microscopy images showed different morphologies and sizes of MoOx particles. MoO3 formed platelet particles that were larger than those observed for MoO2. MoO3 showed stable thermal behavior until approximately 800 °C, whereas MoO2 showed weight gain at approximately 400 °C due to the fact of re-oxidation and oxygen uptake and, hence, conversion to stoichiometric MoO3. Electrochemically, traditional performance was observed for MoO3, which exhibited a high initial capacity with steady and continuous capacity fading upon cycling. On the contrary, MoO2 showed completely different electrochemical behavior with less initial capacity but an outstanding increase in capacity upon cycling, which reached 1600 mAh g−1 after 800 cycles. This outstanding electrochemical performance of MoO2 may be attributed to its higher surface area and better electrical conductivity as observed in surface area and impedance investigations.
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