Boychuk A. Structure, electrophysical and intercalation properties of LiMn2-xFexO4 spinel systems of different morphology

The thesis studies the effect of the iron substitution on structure, morphology, electrophysical and electrochemical properties of lithium-manganese spinel synthesized by ceramic and sol-gel methods. It is shown that the formation of single phase spinel is possible at the temperature of 1070 K for sol-gel synthesis and 1270 K for ceramic method, formation of divalent iron cations was fixed in okta-sublattice, which increases the electrical conductivity of spinel. Based on impedance studies of current sources with cathode based on LiMn2-xFexO4 compounds changes of the conductivity properties of the passivation films and the cathode mixture were fixed in the first cycle of discharge. It is shown that at the initial level of discharging the growth of passivation film resistance took place, which is associated with the accumulation of lithium ions on the cathode surface. It was found out that at the same time cathode compositions conductivity increases with the degree of lithiation. The comparison of these results with the experimental values of constant lattice in the process of lithium intercalation allowed to offer three-stage model of electro-stimulated introduction of lithium ions. Comparison of the diffusion coefficient of ions Li + obtained by SEI methods (10-13 - 10-11 cm2/s) and GITT (10-12 - 10-11 сm2/s) has shown that spinel systems of LiMn2-xFexO4 with different morphology can be successfully used in lithium electrochemical power sources of high capacity and power.