A systematic investigation of the possibility of Fe based cathodes with 2 Li per 1 Fe atom electrochemical cycling was undertaken. In such cathodes, both the Fe2+/Fe3+ as well as the Fe3+/Fe4+ redox couples are to be utilized. Our study was focused on 2 model structures with Fe exclusively in octahedral, LiFeTiO4, or tetrahedral, LiFeO2 - tunnel, environments. The target compounds were prepared via ion exchange from appropriate intermediate phases with larger alkali cations. Structural motifs were preserved during the ion exchanges as confirmed by powder X-ray diffraction measurements.The theoretical specific capacity of LiFeO2 for the case of 2 Li cycling is 526.6 mAh/g, much greater than conventional Li-ion cathode materials. Doped LiFe1-xMxO2 (M = Co, Mn, and Ni) samples were prepared to improve electronic conductivity. Cyclic voltammetry (CV) measurements revealed multiple electrochemical processes during the charge/discharge cycle of these doped materials. The Fe3+/4+ redox couple is the only feasible explanation for the charging peak at 4.5 V. Reaction with the EC:DMC electrolyte begins at 4.6 V. Li intercalation events are observed on CV during the material discharge. The CV results confirm the validity of the approach and feasibility of oxide cathode material utilizing Fe3+/4+ redox couple.Chemical Li intercalation into the LiFeO2 tunnel structure resulted in Li1.57(5)Fe1.00O2 stoichiometry without destroying the structure. Li intercalation occurs at ~2.4 V, as was determined electrochemically. Mossbauer spectroscopy was utilized to determine the Fe oxidation state in the Li intercalated and deintercalated compounds. The tunnel LiFeO2 polymorph is the very first compound demonstrating accessibility of both redox couples, Fe2+/Fe3+ as well as Fe3+/Fe4+, in one compound for electrochemical cycling.

LiFeO<sub>2</sub> � tunnel: The first multiple electrons transfer Fe based cathode compound

246th National Meeting (2013)

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LiFeO2 � tunnel: The first multiple electrons transfer Fe based cathode compound

LiFeO₂ � tunnel: The first multiple electrons transfer Fe based cathode compound