Recent progress, challenges and prospects of electrolytes for fluoride-ion batteries

In the development of new electrochemical concepts for the fabrication of high-energy-density batteries, fluoride-ion batteries (FIBs) have emerged as one of the valid candidates for the next generation electrochemical energy storage technologies, showing the potential to match or even surpass the current lithium-ion batteries (LIBs) in terms of energy density, safety without dendritic grains, and elimination of dependence on scarce lithium and cobalt resources. However, the development of FIBs is still in its infancy and their performance is far from satisfactory, with issues such as the lower fluoride-ion conductivity of the electrolytes and the reversibility of the electrodes hindering their commercialization. Previous reviews have mainly focused on inorganic solid electrolytes with a brief emphasis on the development of various fluoride-ion conductors and their ion-conducting properties. Therefore, this review summarizes the current developments in various electrolytes, a systematic overview of the current progress for various fluoride-ion electrolytes is presented by beginning with the history, structure and classification of FIBs, ion-transport mechanisms are briefly discussed. Recent advances in different classes of fluoride-ion electrolytes are described. The methods for optimizing the ionic conductivity characteristics of the fluoride-ion electrolytes are highlighted. Finally, an outlook on the future research direction of FIBs is given by highlighting some critical issues, challenges and prospects of fluoride-ion electrolytes.