Fluorinated Graphite as an Efficient Halogen Anion Storage Material in Aqueous Dual-Ion Batteries.

Halogen-based aqueous dual-ion batteries (ADIBs) are highly attractive owing to their environmental benignity and promising electrochemical performance. However, the high reactivity of halogen anions leads to severe side reactions during halogen storage in conventional carbon-based positive electrodes, which hinders the development of practical high-performance ADIBs. Herein, fluorinated graphite (CFx) is conceptually redefined as an efficient halogen anion storage material, departing from its traditional role as a cation intercalation host in alkali-metal batteries. Combined density functional theory calculations and in situ Raman spectroscopy verify the intercalation of [BrF] and [ClF] interhalogen species into CFx interlayers. The optimized structure of [C4F2BrCl] affords a theoretical specific capacity of 623 mAh g-1 for CF0.5. Compared with pristine graphite, this unique electrode mechanism effectively suppresses the formation of free Br2/Cl2, while the expanded interlayer spacing of CFx facilitates the intercalation of halogen anions. Accordingly, the CFx positive electrode exhibits superior rate capability and cycling stability. The practical feasibility is further demonstrated in a soft-packaged Zn/CF0.56 pouch cell. This work not only conceptually redefines CFx from a conventional cation host to a high-efficiency halogen anion storage material, shedding lights on deep science in ADIBs, but also lays a solid foundation to rationally design of advanced electrode materials.