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

The Mössbauer 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 FeIIIO4 tetrahedra. The Mössbauer spectrum of LiFePOx glass has an additional doublet due to distorted FeIIO6 octahedra. Heat treatment of LiFeVPOx and LiFeV0.5POx glasses at a given temperature close to each crystallization temperature causes a marked decrease in the value of Δ, reflecting a decrease in the distortion or an increase in the local symmetry of distorted FeIIIO4 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.