Abstract
The lithium-carbon monofluoride (Li-CF (x) ) couple has the highest specific energy of any practical battery chemistry. However, the large polarization associated with the CF (x) electrode (>1.5 V loss) limits it from achieving its full discharge energy, motivating the search for new CF (x) reaction mechanisms with reduced overpotential. Here, using a liquid fluoride (F)-ion conducting electrolyte at room temperature, we demonstrate for the first time the electrochemical defluorination of CF (x) cathodes, where metal fluorides form at a metal anode instead of the CF (x) cathode. F-ion primary cells were developed by pairing CF (x) cathodes with either lead (Pb) or tin (Sn) metal anodes, which achieved specific capacities of over 700 mAh g(-1) and over 400 mAh g(-1), respectively. Solid-state (19)F and (119)Sn{(19)F} nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman, inductively coupled plasma (ICP), and X-ray fluorescence (XRF) measurements establish that upon discharge, the CF (x) cathode defluorinates while Pb forms PbF(2) and Sn forms both SnF(4) and SnF(2). Technological development of F-ion metal-CF (x) cells based on this concept represents a promising avenue for realizing primary batteries with high specific energy.