Influence of iron doping on structure and electrochemical properties of Li 4 Ti 5 O 12

Iron doped lithium titanates Li4+z-3yTi5-zFez+yO12 (0 ≤ z + y ≤ 0.3) have been synthesized and characterized by X-ray diffraction, scanning and transmission electron microscopy, 57Fe Mossbauer spectroscopy, and cyclic voltammetry. Their performance as anode materials for lithium-ion batteries was studied in a wide potential range (0.01 − 3 V). Rietveld refinements and 57Fe Mossbauer spectroscopy data show that iron cations occupy both tetrahedral 8a and octahedral 16d sites in the spinel structure. At that, iron occupancy of the octahedral sites is approximately twice as much as the occupancy of the tetrahedral ones. Occupancy of octahedral sites by Fe3+ ions increases after cycling. Li4+z-3yTi5-zFez+yO12 (z + y = 0.2) exhibits higher electrochemical capacity at high current densities than the pristine Li4Ti5O12. Moreover, capacity of doped material increases after cycling at high current densities.