Lithium-induced conversion reaction in wüstite Fe1−xO studied by 57Fe Mössbauer spectroscopy

Fe1−xO wüstite as negative electrode material for Li-ion batteries has been studied. The aim of this work is to get a better understanding of the insertion mechanism involved during reduction/oxidation processes. Electrochemical tests have been done in Swagelock™ cells and shown a high specific capacity of 800 A h/kg for the first discharge. X-ray diffraction and 57Fe Mössbauer spectroscopy provide us valuable information on both local and long range order. Hence, Li reaction with wüstite induces formation of highly divided metallic iron (α-Fe and nano-Fe) and Li2O with a small amount of Fe2O3 occurring in a diffusion layer at the surface of the primary particles. Based on the X-ray and Mössbauer spectroscopic analyses, a core–shell model is proposed in order to explain the irreversible capacity of about 1 Li observed at the first cycle. It involves cation diffusion induced by lithium acting as an ‘electronic pressure’.

57Fe Mössbauer spectrum at 300 K of the pristine Fe1−xO material. Three doublets centered at about 1 mm/s are inferred to FeII and the doublet centered at 0.55 mm/s lies in the range of FeIII. The areas of the 3 doublets of FeII are in the ratio 51:31:18. The impurity (2%) of the overall absorption is characterized by a doublet centered at δ = 0 mm/s with Δ = 1.68 mm/s corresponding to inner lines 3 and 4 of the sextet of to α-Fe as impurity.Figure optionsDownload as PowerPoint slide