Structural and electrochemical properties of Li(Fe, Co)xMn2-xO4 solid solution as 5 V positive electrode materials for Li secondary batteries

Solid solutions, Li( Fe, Co)(x)Mn2-xO4 (0 less than or equal to x less than or equal to 0.5 for Fe, 0 less than or equal to x < 1.0 for Co) were synthesized by solid state reaction at 1023-1073 K in O-2 atmosphere. The compositional dependence of lattice parameters and cation distribution was studied by neutron diffraction Rietveld refinement. It was revealed that Fe and Co partially occupied tetrahedral 8a sites and the 1 : 3 and 1 : 1 ordering did not occur on Fe (Co) and Mn ions in octahedral 16d sites. X-Ray absorption fine structure (XAFS) analysis showed the variation of valences and metal-oxygen interatomic distances of Mn, Fe, and Co. The Fe-O distance was longer whereas the Co-O distance was shorter compared to the averaged M-16d-O-32e distance calculated from the lattice parameters. Charge and discharge properties were studied in voltage range 3.0-5.3 V vs. Li/Li+.