Dicationic ionic liquids with difluorophosphate anions

Abstract

Dicationic ionic liquids can be diversely designed by tuning the spacer and cationic center structures. Their potentially superior features compared to conventional ionic liquids include enhanced thermal stability and a wide potential window, making them promising candidates as electrolytes for secondary batteries. However, there are relatively few reports on dicationic ionic liquids, and the relationship between their structure and physical properties remains largely unexplored. In this study, a series of dicationic ionic liquids are synthesized using PO₂F₂⁻. The effects of cationic, anionic, and linker structures on their physical and electrochemical properties are discussed through different analytical and computational methods. The cationic structures examined include pyrrolidinium, ammonium, and imidazolium, while the anionic impact was pursued by comparing the case with BF₄⁻. The dicationic ionic liquid with an ether linker emerged as a promising candidate due to its high ionic conductivity and wide electrochemical window among all the tested salts.