In addition to further developments in Li-ion batteries, new research directions are focusing on further
improvements of the battery performance. Alternative technologies are investigated based on different
chemistries using, e.g., sodium, magnesium or chloride as charge transfer ions in secondary batteries.
Batteries based on a fluoride ion shuttle (fluoride ion battery) are an interesting alternative to Li-ion
batteries as they can theoretically provide substantially higher volumetric energy densities compared to
Li-ion batteries. Recently, the principle of a secondary battery based on a fluoride ion shuttle has been
demonstrated. Here, the electrolyte is one of the key components to obtain good cycling properties
(e.g., resulting from fast F conduction in fluoride ion batteries).