EDTA as chelating agent for sol-gel synthesis of spinel LiMn2O4 cathode material for lithium batteries

Ethylene diamine tetra-acetic acid (EDTA) was used to prepare spinel LiMn2O4 at 650 degrees C. The prepared sample by EDTA (E-LiMn2O4) is compared with another spinel sample (C-LiMn2O4) prepared by citric acid as a common chelating agent at the higher temperature (800 degrees C) adjusted to obtain the same size and shape of the particles as in (E-LiMn2O4) 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 LiMn2O4 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 LiMn2O4 structure. Li-7 MAS NMR and XPS spectra show that the amount of Mn4+ is larger in LiMn2O4 sample prepared by citric acid. LiMn2O4 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 Mn3+ ions, that are not modified by the choice of chelating agent. (C) 2017 Elsevier B.V. All rights reserved.