A Bioinspired Antifreezing Electrolyte Enabling Stable and Low-Temperature Fluoride-Ion Batteries via Hydrogen-Bond Reconfiguration.

Fluoride-ion batteries (FIBs) are appealing for their high theoretical energy density and low cost, wherein aqueous electrolytes provide the exceptionally high fluoride-salt solubility and fast ion transport. However, the strong H2O-H2O hydrogen-bond network promotes the proton/hydroxide shuttling and leaves the reactive free water at interface, leading to parasitic reactions, corrosion and active-material dissolution, which severely limit cycling stability. Here we show that reconfiguring the hydrogen-bond network of water offers a molecular-level pathway to stabilize aqueous FIB chemistry. We report a bioinspired hydrogel electrolyte by introducing hyaluronic acid (HA) into CsF aqueous electrolyte, together with ethylene glycol (EG) as an antifreezing co-solvent. HA reorganizes the hydrogen-bond network to immobilize free water and suppress water activity, while HA/EG jointly regulate the solvation environment of F-, reducing the hydration level and facilitating the interfacial fluoride transfer. The HA-based electrolyte forms a robust, chemically rich CEI containing organic (O/N-containing) and fluoride-rich inorganic components, which mitigates interfacial side reactions and suppresses active species dissolution. A CuF2||Pb full cell delivers the stable cycling with a ∼0.5 V discharge plateau and retains over 100 mAh·g-1 after 160 cycles, and further demonstrates the reversible FIB operation down to -20°C for the first time.