LiFeVO4 – cathode material for litium chemical power sources

Abstract

LiFeVO 4 was synthesized chemically. Electroactive composite on its base was prepared by mechanical mixing of LiFeVO 4 and graphite in mass ratio 7:1. Lithium power sources numbered I and II with the prepared composites basedcathode were constructed. In the first case we used two lithium anodes and LiFeVO 4 –graphite based cathode (cell I ). In the second case surface of lithium anodes was covered by pressed graphite layer (cell II ). Cells charge – disсharge characteristics were determined at the external circuit resistance equal to 300 Ohms. The results of research of these cells indicate high values of discharge capacities and energies. At the primary discharge, the internal resistance was sufficiently low. During the charge of the cell I there were relatively high charge currents, which after a short time of charging began to grow very rapidly. Evidently the reason for this is dendrite formation processes on the surface of the lithium electrodes. Generated dendrites lead to an internal short circuit in the cell that causes sharp increase in current. It also led to low values of discharge capacity and energy at the secondary discharge. Also, after overcharging, the internal cell resistance increases. On the other hand, high charging currents indicate a high rate of lithium ions diffusion in the electroactive material of a positive electrode. Discharge characteristics of cell II were slightly lower. Discharge current and voltage decrease faster than for cell I . The discharge characteristics of cell II after the charge were very low due to the fact that the amount of electricity consumed by the charge was very small. The discharge characteristics after the charge were very low due to the fact that the amount of electricity used for charge was very small. Most likely the reason for this is the formation of a passivation film on the lithium electrode surface. As a result, the direct contact between graphite and lithium becomes impossible and graphite acts as an additional separator. Internal resistance increases and the process of functioning of cell II complicates. The obtained results indicate the prospect of LiFeVO 4 as an electrically active material for rechargeable lithium current sources. Keywords: lithium-ferrum (III) vanadate, lithium power sources, charge-discharge properties.