In situ X-ray absorption spectroscopy study of lithium insertion in a new disordered manganese oxi-iodide

Abstract

Mn K-edge X-ray absorption measurements were carried out on an amorphous manganese oxi-iodide (Li 0.60Na 0.16MnO 2.33I ≈0.05) as cathode material in plastic lithium batteries. X-ray absorption spectroscopy experiments were performed in situ for every lithium intercalation increment Δ x≈0.10 per formula unit along a discharge with 0≤ x≤0.67. The X-ray absorption near edge structure (XANES) spectra demonstrate a smooth decrease of Mn valence with in-situ reduction, confirmed by a monotonous increase in Mn–O distance from extended X-ray absorption fine structure (EXAFS). The first-shell octahedral coordination of manganese is hardly affected by lithium insertion, while the evolution of the Mn–Mn coordinence shows a trend towards the formation of MnO n polyhedra chains on deep discharge. The material discharged to an average manganese valence 3.25+ showed negligible static Jahn–Teller effect. Together with the inherent flexibility of disordered structures towards intercalation and bond length changes, this is probably a major cause of the stability of this oxi-iodide on cycling in lithium batteries.