Relaxation structure analysis of Li inserted γ-Fe2O3

γ-Fe2O3 has a spinel structure with cation vacancy and is expected to perform as a favorable electrode material for secondary lithium-ion battery. When lithium is inserted electrochemically into γ-Fe2O3, prolonged potential change is observed after the insertion. In this study, we inserted various amount of Li into γ-Fe2O3 (x = 0.66, 1.1, 1.5 in terms of LiXFe2O3), then made the circuit open, measured X-ray diffraction (XRD) patterns at various elapsed time, and analyzed the crystal structure change of γ-Fe2O3 with time by the Rietveld method. The X-ray Rietveld analysis revealed that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and after lithium insertion, the iron occupancy of 8a site increased and that of 16c site decreased gradually with relaxation time. It is indicated that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically.

► γ-Fe2O3 shows prolonged potential change after electrochemical Li insertion.
► We analyzed γ-Fe2O3 crystal structure by the XRD Rietveld method after Li insertion.
► Fe occupancy of 8a site increased and that of 16c site decreased with elapsed time.
► It is suggested that Li migrated from 8a site to 16c site after Li insertion.
► Li prefer 8a site to occupy kinetically and prefer 16c site thermodynamically.