Alkaline Earth Metals As Anode for High Energy Rechargeable Fluoride Ion Batteries
Alkaline earth metals have recently attracted much attention for their employment in energy storage technologies due to potentially high energy density, low cost and environmental friendliness. Hence, in this study Ca and Ba pure metals were chosen and tested as anode in rechargeable FIB system. CaxBa1-xF2 (x ~ 0.5), a highly ion conducting metastable fluoride compound, was selected and synthesized via high energy mechanical milling route as fluoride ion conducting electrolyte. Powder X-ray diffraction confirms the formation of solid solution and electrochemical impedance measurement of CaxBa1-xF2 shows ionic conductivity in the order of 10-4 S.cm-1 at elevated temperature around 200 0C, which is in agreement with earlier report . The assembly of all-solid-state electrochemical FIB cells was carried out with Ca or Ba as anode, selected metal fluorides (BiF3, CoF3, and CuF2) as high voltage cathode, and CaxBa1-xF2 (x ~ 0.5) as electrolyte. The cells were assembled in the charged state and electrochemically tested at ~ 200 0C. Initial results showed that the specific capacities of Ca/BiF3 and Ca/CuF2 cells for the first discharge are about 260 mAh/g and 350 mAh/g, respectively. These capacities are about 86% (in case of BiF3) and 66% (in case of CuF2) of their theoretical specific capacities and higher than those of Ce/BiF3 and Ce/CuF2 systems reported previously . Electrode analysis together with cycling behaviour reveal the fluoride ion transfer between anode and cathode, as well as the cyclability of alkaline earth metal based FIB system. Further structural and electrochemical characterization will be presented and discussed.
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