RESUMO
Spinel oxides with composition LiMn2-xMxO4 (M, a transition metal) are intensively studied due to their remarkable electrochemical properties. This study deals with cathode materials based on the lithium iron manganese oxide LiFe0.5Mn1.5O4 synthesized by different methods (sol-gel, in solution and hydrothermal) in order to obtain samples with various morphologies. SEM results show microspheres, composed of nanosized/submicrometer-sized subunits, microrods with a less porous surface, and finally nanoparticles that form micro-sized aggregates. The samples obtained by both solution and hydrothermal methods provided the best electrochemical behavior. In all cases, the coulombic efficiency is around 90%, and it remains constant during the tested cycles. Specific capacities remain stable between 95% and 98% of capacity retention after series of cycles in samples formed by microspheres or micro-size aggregates. These values are notably higher than those obtained for the samples with particles of heterogeneous size (49%). A LiMn1.5Fe0.5O4/Li2MnO3 composite has been prepared by the solvothermal technique in order to increase its capacity and energy density. These cells show a good cyclability at different current densities. All cells based on these LiFe0.5Mn1.5O4 cathodes recover their discharge capacity when the current density returns to C/10.
