Synthesis, structure, and electrochemical properties of LiFeV2O7
Résumé
The structure of a novel compound, LiFeV2O7, has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the non-centrosymmetric monoclinic Cc space group. The structure can be described as a layered type compound alternating (Li,Fe)–O sheets and V–O chains that are perpendicular to the [101] direction. Within the (Li,Fe)–O sheets, “hexagonal” holes are formed and assembled into tunnels running parallel to the [201] direction and hosting the vanadium atoms. Original (V4O14)8– strings are observed within the structure in association with well-known (V2O7)4– pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV2O7 displays a reversible insertion–deinsertion mechanism for Li+ ions. The theoretical capacity for the insertion of one Li+ into LiFeV2O7 reaches 97 mAh/g. When the compound is cycled between 3.50 and 2.35 V versus Li+/Li, the electrochemical curve displays an initial capacity of 100 mAh/g, with 85% of this capacity retained after 60 cycles. No evidence of the formation of Fe4+ upon oxidation to a high voltage was observed. LiFeV2O7 represents the first reported phase in the Li2O–Fe2O3–V2O5 ternary diagram with electrochemical activities.