Synthesis and characterization of novel complex iron oxides with layered and tunnel structures.

摘要

Novel cathode materials for lithium ion batteries were synthesized via lithium for sodium ion exchange from the known compounds, ss-NaFeO 2 and NaFeTiO4. The resulting lithium analogs of these known sodium compounds, T-LiFeO2 and LiFeTiO4, contain tunnel-like structures that were characterized using Rietveld refinement of Powder X-ray diffraction, electrochemical measurements, Mossbauer spectroscopy, thermogravimetric analysis, and inductively coupled plasma spectroscopy. Similarly characterized, alpha- and ss-NaFe2O3, with a double layered rock salt structure, were synthesized for the first time as a bulk powder using an oxygen pressure regulation method that provided the appropriate conditions for the two polymorphs to form.;Further, investigation into T-LiFeO2 and NaFe2O 3 by doping other transition metals into the iron position, to control specific properties of the two materials was performed with success. T- T-LiFeO 2 and the parent phase, ss-NaFeO2, were doped with up to 0.1 and 0.15 parts of cobalt per formula unit respectively. NaFe2O3 was successfully doped with cobalt up to 0.5 moles with pure phases of both the alpha-NaFe 1.5Co0.5O3 and ss-NaFe1.5 Co0.5O3 forming. Manganese doping into NaFe 2O3 also showed the formation of the alpha- phase.;Probing the Fe3+/4+ redox potential of both T-LiFeO 2 and LiFeTiO4 resulted in the decomposition of each. The cobalt doped T-LiFeO2 though did show a greater possibility of cycling at Fe3+/4+ redox potential, but also resulted in a reaction with the organic electrolyte. Chemical deintercalation of T-LiFeO 2 and LiFeTiO4 were performed with resulting in the decomposition of LiFeTiO4. T-LiFeO2, indicated successful lithium deintercalation with preliminary Mossbauer results illustrating Fe 4+ formation. Both LiFeTiO4 and T-LiFeO2 successfully cycled electrochemically at the Fe2+/3+ redox potential, with the new calcium ferrite structure polymorph LiFeTiO4 cycling 17 % higher capacity than the previously reported spinel and rock salt structure compounds.