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

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 Δx≈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.