Lithium insertion in lithium iron molybdate

We report here, for the first time, facile and reversible insertion/extraction of lithium in LiFe(MoO4)2. A biphasic reaction is observed in the compositional range 0 < x < 0.9 in Li1 + xFe(MoO4)2 with a remarkably flat plateau at an average voltage of 2.68 V due to the redox couple Fe3 +/Fe2 +. An irreversible structural change was associated with lithium insertion. The plateau behavior is reversible with negligible hysteresis (ΔdQ/dV = 0.05 V) and 100% Faradaic efficiency. A reversible capacity of 63 mAh/g is obtained in the voltage window 3.0–2.5 V. When reduction of Mo6 + is also accessed by cycling in the voltage window 3.0–1.0 V, a reversible capacity of ~ 180 mAh/g was obtained at the end of 20 cycles at C/5 rate.

Figure optionsDownload as PowerPoint slideHighlights
► Iron based polyanion channel structure; new host for reversible lithium insertion.
► Fe3 +/Fe2 + couple, flat voltage plateau, high reversibility, very low polarizability.
► Additional reversible capacity by invoking electrochemical activity of Mo6 +.