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

Abstract

ABSTRACT 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 H 2 O−H 2 O 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 CuF 2 ||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.