Mossbauer study of LiFeVPOx as a new cathode material for lithium-ion battery

The Mossbauer spectrum of LiFeVPOx , LiFeV0.5POx and LiFePOx glasses prepared by conventional melt-quenching method for cathode active material is composed of a doublet due to distorted (FeO4)-O-III tetrahedra. The Mossbauer spectrum of LiFePOx glass has an additional doublet due to distorted (FeO6)-O-II octahedra. Heat treatment of LiFeVPO (x) and LiFeV0.5POx glasses at a given temperature close to each crystallization temperature causes a marked decrease in the value of Delta, reflecting a decrease in the distortion or an increase in the local symmetry of distorted (FeO4)-O-III tetrahedra. Heat treatment of LiFeVPOx glass causes an increase in the electric conductivity from the order of 10(-7) to 10(-3) S.cm(-1), together with an increase in the specific discharge-and charge-capacity of a coin-type Li-ion cell from 50 to 150 mAh.g(-1). These results prove that structural relaxation of the glass network causes an increase in the electric conductivity and an increase in the energy density of the Li-ion cell.