Fluoride-ion batteries

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Rechargeable batteries with higher energy densities are fundamental to meeting the ever-increasing requirements of consumer electronics, electric vehicles, and a burgeoning renewable energy economy. With the Li-ion chemistry approaching its thermodynamic limit, new chemistries are being investigated, mostly Li-based. Fluorine, sitting at the opposite end of the periodic table from lithium , is the most electronegative element. Fluoride-ions are therefore electrochemically very stable and possess a large electrochemical stability window. Because of these characteristics, fluoride ion batteries (FIBs) have a theoretical volumetric energy density which is 50% higher than the theoretical value for lithium-air cells, making them the ideal candidate for the next generation of high energy density batteries. However, at this incipient stage, the charge/discharge mechanism at both positive and negative electrodes in FIBs is still poorly understood, a liquid electrolyte for long-term cycling stability has not been identified and a suitable reference electrode has not yet been established. As a result, fluoride ion batteries are still far from reaching the cyclability required for commercial applications.This project aims to investigate suitable metal fluorides to be used as the electrode materials and their charge/discharge mechanism. Ionic-liquid based electrolytes will be developed to improve the overall performance of FIBs. To this end, the electrochemical phase evolution and mass/charge transport of transition metal fluoride cathodes will be investigated, by characterizing the structural and morphological changes during cycling through ex-situ TEM/SEM (i.e. transmission electron microscopy and scanning electron microscopy). In addition, new in-situ TEM and X-ray techniques will be explored for the collection of time-resolved structural and chemical data under realistic battery conditions. An in depth study on the electrolyte will also be required in order to achieve a perfectly working battery. Hence, an optimum electrolyte composition using ionic liquids will be investigated in order to improve the stability and ionic conductivity of the battery. Particular attention will be focused on tailoring the electrode surface compositions to mitigate dissolution and side reactions. The overall project will involve the use of surface/interfacial characterization techniques including impedance spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman, and scanning electron microscopy with energy disperse X-ray spectroscopy (SEM-EDX).This project falls within the EPSRC Energy research area. The aim of this theme is for the UK to meet its environmental and energy targets.