Observation of electrochemically active Fe3+/Fe4+ in LiCo0.8Fe0.2MnO4 by in situ Mössbauer spectroscopy and X-ray absorption spectroscopy

Abstract

LiCo_0.8Fe_0.2MnO₄ has been investigated as an active material for the positive electrode in lithium-ion batteries (LIBs) with a discharge potential of around 5 V (vs. Li⁺|Li). After synthesis by a Pechini based sol–gel route, the structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy, ⁷Li MAS NMR spectroscopy, and ⁵⁷Fe Mössbauer spectroscopy. With galvanostatic cycling, it was possible to obtain a specific discharge capacity of 117 mA h g⁻¹, which is more than 80% of the theoretical capacity. The lithium extraction/insertion mechanism has been characterized by in situ synchrotron powder diffraction. The reversible oxidation process of Fe³⁺ to Fe⁴⁺ has been observed by in situ Mössbauer spectroscopy and in situ XAS measurements.