Fluoride-ion batteries (FIBs) have recently emerged as a candidate for the next generation of electrochemical energy storage technologies. On paper, FIBs have the potential to match or even surpass lithium-metal chemistries in terms of energy density, while further eliminating the dependence on strained resources, such as lithium and cobalt.
Among the available candidates, fluoride-ion batteries (FIBs) are a promising technology because of their high theoretical energy density and utilization of abundant and widespread materials. However, FIBs present several new challenges that have prevented them from reaching commercialization.
Fluoride ion batteries (FIB) are a promising post lithium-ion technology thanks to their high theoretical energy densities and Earth-abundant materials. However, the flooded cells commonly used to test liquid electrolyte FIBs severely affect the overall performance and impede comparability across different studies, hindering FIB progress.
The concept of the fluoride-ion battery was first demonstrated using conversion-type electrodes. 10 In the context of FIBs, the conversion reaction involves the electrochemical transformation between any metal and its corresponding metal fluoride M + xF − ↔ MF x + xe −.
Batteries release energy as electrons move from a material with a high Fermi level (anode) to one with a low Fermi level (cathode). In a fluoride-ion battery, charge neutrality is maintained by the concurrent removal of fluoride ions from the cathode material and insertion of fluoride ions in the anode material (Figure 2).
The motivation behind developing liquid fluoride-ion electrolytes for batteries is to achieve better ionic conductivity in the electrolyte and a wider ESW. Although alkali metal fluorides are readily available, their solubility in commonly used high-boiling organic solvents is usually less than 0.05 M [ 204 ].