Intrinsic instability of Fe4+ in electrochemically oxidized ramsdellite and orthorhombic Li1-xHxFeO2

The cathodic materials r-Li0.8H0.2FeO2 (ramsdellite-type) and o-Li0.7H0.3FeO2 (orthorhombic form) were synthesized in an autoclave by reaction of iron oxohydroxides with lithium ethoxide in anhydrous ethanol. The compositions of the phases were determined both by means of elemental analyses and density measurements. The crystal structures of r-Li0.8H0.2FeO2 and o-Li0.7H0.3FeO2 were determined by the Rietveld method. The powders were made of homogeneously distributed submicronic needles. Electrochemical tests of the Li1-xHxFeO2/Li systems were carried out along with X-ray diffraction and Mossbauer spectroscopy. The results from all the physical techniques employed taken together showed the instability of Fe4+ formed during the recharge of the Li1-xHxFeO2 materials, forbidding cycling on the Fe4+/Fe3+ electrochemical couple.