Electrolyte Design by Synergistic High-Donor Solvent and Alcohol Anion Acceptor for Reversible Fluoride Ion Batteries

Abstract

Fluoride ion batteries (FIBs) are regarded as one of the most promising candidates for next-generation energy storage systems to achieve lower cost and higher energy density. However, the appropriate electrolyte design strategy is still lacking for FIBs to simultaneously settle the issues of fluoride salt dissolution and metal cation shuttle. Herein, a novel fluoride ion shuttle electrolyte with the synergistic high-donor solvent (N, N-dimethylacetamide, DMA) and alcohol anion acceptor (benzyl alcohol, BA) is developed. BA enables the promotion of solubility of inorganic fluoride salt (CsF). Meanwhile, benefiting from the re-configuration of hydrogen bonding network by DMA, the solvation structures of anions and cations are regulated with reduced hindrance to F⁻ shuttle and mitigated dissolution of active material. This electrolyte formation achieves superior interfacial stability with cathode, high F⁻ conductivity (2.05 mS cm⁻¹), and transference number (0.53). After matching CuF₂ cathode and Pb anode, the full cell exhibits the highly reversible conversion reaction process with an initial discharge capacity of 300.8 mAh g⁻¹ and a reversible capacity of 245.5 mAh g⁻¹ after 43 cycles. This study proposes a solution to high-performance rechargeable FIBs at room temperature by synergistically manipulating the anionic and cationic solvation chemistry.