An alluaudite Na2+2Fe2−(SO4)3(x= 0.2) derivative phase as insertion host for lithium battery

A new desodiated derivative compound, Na0.89Fe1.8(SO4)3, was prepared by the chemical oxidation of alluaudite Na2.4Fe1.8(SO4)3 phase using NOBF4 as oxidant. The structure and valency of Fe were characterized by X-ray diffraction (XRD) and 57Fe Mössbauer spectroscopy. Intercalation behavior of lithium ions in the structure of Na0.89Fe1.8(SO4)3 was gauged by electrochemical analyses and ex-situ X-ray diffraction. A high capacity of 110 mAh g− 1 at 0.1 C was obtained with a good rate kinetics within a range of 0.1–10 C(1 C = 118 mAh g− 1) involving a high Fe3 +/Fe2 + redox potential of 3.75 V (vs. Li/Li+). These results confirmed that the Na2.4− δFe1.8(SO4)3 framework was stable even after oxidation and forms a new competitive cathode for the reversible intercalation of lithium ions.