Preparation of lithium manganese oxides containing iron

Preparation of LiFeO₂-Li₂MnO₃ solid solution has been attempted using hydrothermal and solid state reactions. Three 10% Fe-doped Li₂MnO₃ samples (Fe/(Fe + Mn) = 0.1) with different average particle sizes could be obtained by both methods. The initial charge capacities for these cathodes were sensitive to the preparation method; the capacity up to 4.3 V is 45 mAh/g for the hydrothermally-obtained sample, 24 mAh/g for the post-annealed sample after hydrothermal-treatment at 673 K, and 6 mAh/g for the sample obtained by solid state reaction at 1173 K. ⁵⁷Fe Mössbauer spectra detect the oxidation of Fe³⁺ to Fe⁴⁺/reduction of Fe⁴⁺ to Fe³⁺ after initial charging/discharging for the hydrothermally obtained sample. The observed Fe^3+/4+ redox voltage is between 4.0 and 4.5 V which is lower than that predicted (5 V) for Fe-doped LiMn₂O₄. This suggests that hydrothermally synthesized Fe-doped Li₂MnO₃ is an environmentally-friendly candidate as cathode material, involving a Fe^3+/4+ redox reaction for rechargeable lithium batteries.