Low temperature synthesis and electrochemical characteristics of LiFeO₂ cathodes

Two rechargeable polymorphs of LiFeO₂ have been synthesized at low temperatures of less than 250 °C via a novel H⁺/Li⁺ ionic-exchange reaction in an alcoholic solution using stoichiometric amounts of lithium alkoxide and iron oxyhydroxide as the starting materials. The reaction, which proceeded in a topotactic manner, resulted in new polymorphs in the LiFeO₂ family with similar crystal structures to the parent materials. Two types of LiFeO₂, the corrugated layer and goethite type, were rechargeable in lithium cells with a cycling capacity of 0.2-0.4 Li/LiFeO₂ in the 1.5-4.5 V range, unlike the other six non-rechargeable polymorphs reported so far. A preliminary X-ray diffraction study on structural changes in the cathode during cycling showed a minimal lattice parameter change for corrugated layer LiFeO₂ and a noticeable a-lattice shrinkage/expansion of about 1% for goethite-type LiFeO₂.