Study of various ("super iron") MFeO₄ compounds in Li salt solutions as potential cathode materials for Li batteries

In this work we studied the possibility of using Fe⁺⁶ "super iron" compounds, including BaFeO₄,K ₂FeO₄,CuFeO₄, and SrFeO₄ as potential cathode materials for rechargeable Li batteries, and their behavior in several nonaqueous Li salt solutions. Classic electrochemical techniques, such as cyclic voltammetry and chronopotentiometry combined with X-ray photoelectron spectroscopy, X-ray diffraction, Mössbauer spectroscopy, atomic adsorption, atomic emission, in situ and ex situ atomic force microscopy imaging, and diffuse reflectance Fourier Transform infrared spectroscopy were used in order to obtain a full picture of the electrochemical behavior of these compounds. Fe⁶⁺ compounds such as K₂FeO₄ and BaFeO ₄ are reduced in the presence of Li ions to Fe³⁺ compounds. Fe₂O₃,Li₂O, and K₂O or BaO are formed in amorphous or nanocrystalline structures. The reaction is partially reversible, i.e., Fe⁶⁺ compounds can be reformed by oxidation. The mechanisms of the lithiation-delithiation of these systems and what limited their reversibility are discussed.