Maghemite-based anode materials for Li-Ion batteries: The role of intentionally incorporated vacancies and cation distribution in electrochemical energy storage

Anode materials for Lithium-Ion Batteries (LIBs) based on Mo- and V-doped maghemite were prepared by the sol-gel route. High-Resolution Transmission Electron Microscopy (HRTEM) showed the formation of isotropic nanoparticles. The X-ray Photoelectron Spectroscopy (XPS) revealed the presence of Fe3+ and Mo6+ or V4+ for Mo- or V-doped samples, respectively. Rietveld refinement of X-ray Diffraction (XRD) patterns revealed the distribution of Mo6+ and V4+ cations and showed increase in vacancies. The crystallite size resulted from Rietveld adjustments was in agreement with the HRTEM results. The Extended X-ray Absorption Fine Structure (EXAFS) showed a shrinkage of Fe–O–Fe linkages which is responsible for the reduction of the maghemite cell parameter which agreed with the structural analysis from XRD. The X-ray Absorption Near Edge Structure (XANES) confirmed XPS analysis that Fe3+ is present. Coin cells were assembled and galvanostatic cycling was implemented at various charge-discharge current densities, cyclic voltammograms of Li-ions insertion/extraction processes were obtained and the Electrochemical Impedance Spectroscopy (EIS) was investigated. An exceptional cyclic stability and storage capacity for the V-doped maghemite was observed for low current density. The Mo-doped maghemite has higher capacity retention at high current densities.