Nonflammable Fluorinated Electrolyte Realizing High Voltage Anode-Free Zn Dual-Ion Batteries

Due to the low decomposition potential of H₂O and its corrosive effect to Zn foil, the Zn metal battery with aqueous electrolytes operates within a narrow electrochemical window and exhibits low anode utilization ratio. Fluorinated carbonate ester, exhibiting low highest occupied molecular orbital (HOMO) energy level, is suitable for constructing high-voltage batteries, yet its application in Zn metal battery has been scarcely explored. Herein, we propose an electrolyte based on fluorinated solvents and ethoxy (pentafluoro) cyclotriphosphazene (PFPN) additive, which exhibits a high decomposition voltage of 2.75 V in Zn batteries. The fluorinated carbonate esters possess non-flammability and exhibit reduced solvation capacity which in turn promotes the incorporation of anions into Zn²⁺ solvation shell. Consequently, an anion-derived interface layer is formed on Zn anode, aiding the compact and planar growth of deposited Zn. Therefore, the Zn//Zn cell exhibits an impressive Zn utilization of 91 % for 140 h, a level seldom reported previously. Benefitting from the oxidation resistant solvents and cathode-electrolyte interface layer formed by PFPN additive, the Zn//graphite dual-ions battery shows an extended cycling life of 1000 cycles. Furthermore, an anode-free cell was constructed and stably operated for 100 cycles, with a notably high average discharge midpoint voltage of 1.84 V.