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

Highlights: • Intentional vacancies are generated by doping maghemite with Mo6+ and V4+. • Cation and vacancy distributions are studied using XRD and XAFS techniques. • CV and EIS for coin cell batteries with anodes from Mo and V-doped maghemite are studied. • Electrochemical performance is discussed in terms of structural properties of such anode materials. -- Abstract: 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.