Iron Fluoride Hydrate As Cathode Material for Sodium Ion Secondary Batteries and Its Characterization

In recent years, numerous efforts have been made to develop rechargeable batteries to use for large scale applications such as in electric vehicles (EVs), hybrid electric vehicle (HEV) and plug in hybrid electric vehicles (PHEVs). Lithium ion batteries have been the most popular and widely used batteries in portable devices like cell phones, laptops, etc. However, it has some constraints to be used for large scale applications as the cost for the raw materials for lithium is expensive. There have been ongoing studies searching for alternative shuttle ions and sodium can be one of the possible substitutes since it is more abundant and cheaper. Besides, transition metal fluorides are expected to deliver larger capacities compared to metal oxides as they can utilize more than one oxidation states of transition metal ions resulting in accommodating more than one shuttle ions, which is Na.

Iron fluoride hydrate was prepared at low temperature with non aqueous precipitation method using ionic liquid as a soft template. Iron fluoride hydrate with in situ coating of multi-walled carbon nanotubes (MWNT) and reduced graphite oxide (rGO) were also prepared. Single phase iron fluoride hydrate was successfully prepared and it was confirmed by X-ray diffraction. Morphologies of the samples and nanoparticles growth around the MWNTs are observed by SEM. Thermal analysis of iron fluoride hydrate was measured using TGA and in depth analysis on the thermal structural changes were monitored by temperature dependent in situ XRD. Temperature dependent in situ XRD provides valuable information of the structure change and its decomposition mechanism of iron f iron fluoride hydrate at elevated temperature. Electrochemical measurements of iron fluoride hydrate electrodes coated with MWNT and rGO against sodium metal were performed in galvanoststic mode. The cells were disassembled at different discharged and charged potentials for ex situ characterizations e.g. XRD, NEXAFS and XANES to determine the electrochemical reaction mechanism. More details will be discussed at the meeting.