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

The cathodic materials r-Li0.8H0.2FeO2 (ramsdellite-type) and o-Li0.7H0.3Fe O2 (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 dens ity measurements. The crystal structures of r-Li0.8H0.2FeO2 and o-Li0.7H0.3 FeO2 were determined by the Rietveld method. The powders were made of homog eneously distributed submicronic needles. Electrochemical tests of the Li1- xHxFeO2/Li systems were carried out along with X-ray diffraction and Mossba uer spectroscopy. The results from all the physical techniques employed tak en together showed the instability of Fe4+ formed during the recharge of th e Li1-xHxFeO2 materials, forbidding cycling on the Fe4+/Fe3+ electrochemica l couple.