Synthesis and characterisation of new cathode materials for second generation sodium batteries

Abstract

This thesis reports exploratory studies on the synthesis and characterisation of new compounds as cathode materials for second generation sodium batteries, with a particular emphasis on preparing new iron-phosphite and molybdenum oxyfluoride cathode materials. Seven different compounds are hereby reported: the sodium iron fluoro-phosphite of formula NaFe₃(HPO₃)₂[(H,F)PO₂OH)₆], the iron-phosphite Fe₂(HPO₃)₃, the sodium iron-phosphite NaFe(H₂PO₃)₄, the sodium iron phosphate NaFe(HPO₄)(H₂PO₄)₂·H₂O and three molybdenum oxyfluoride compounds of formula Na₂MoO₂F₄, KNaMoO₂F₄ and KMoO₂F₃. The synthesis of these compounds was performed by hydrothermal and solvothermal methods at temperatures ranging from 100 °C to 160 °C. The compounds were then fully characterised using the following techniques: single crystal X-ray diffraction (SXD), powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and electrochemical testing. Magnetic properties have also been studied where appropriate.