A polymer membrane developed at Politecnico di Milano transports fluoride ions through a quasi-solid battery electrolyte at room temperature, reaching an ionic conductivity of up to 1.3 millisiemens per centimeter — a result that removes one of the biggest obstacles to fluoride-ion batteries, a lithium-free chemistry that has long struggled to move ions without heating, Interesting Engineering reported.
The membrane, a gel built from a perfluorosulfonic amide ionomer carrying tetraalkylammonium fluoride groups, functions as a fluoride-exchange membrane, shuttling fluoride ions between electrodes. Researchers modified it with a solvent mixture of 1,3-dioxolane and dimethyl sulfoxide, which swells the ionomer and opens pathways for the ions to move.
DMSO and DOL Swell the Membrane to Move Fluoride Ions
Electrochemical impedance spectroscopy measured the conductivity at up to 1.3 millisiemens per centimeter at room temperature. Molecular dynamics simulations run by the team showed that dimethyl sulfoxide acts as a polar swelling agent, a key detail in why the quasi-solid material conducts. The researchers describe the membrane as the first fluoride-exchange membrane developed for this battery type, drawing on established proton-exchange and anion-exchange membrane concepts.
In experimental coin cells built with lead and lead fluoride electrodes, the electrolyte demonstrated reversible fluorination and defluorination — the processes that move fluoride ions into and out of electrode materials during charging and discharging. The cells cycled stably for more than 50 cycles at room temperature at a current density of 0.1C.
600 Wh/kg Potential Set Against 150–250 Wh/kg for Lithium-Ion
Fluoride-ion batteries attract interest because fluoride is abundant and the conversion-based chemistry theoretically offers far higher energy density than lithium-ion. The research team cited a potential of around 600 watt-hours per kilogram, compared with roughly 150–250 Wh/kg for standard lithium-ion batteries — though those figures represent potential, not performance demonstrated by the experimental cells.
The university says the quasi-solid membrane is non-flammable, a potential safety advantage for energy storage. The coin-cell tests, however, do not establish the fire safety or commercial performance of a complete battery system.
Coin Cells Cycle 50 Times; Complete Batteries Remain Distant
Possible applications include stationary energy storage, electric vehicles and aviation. But the chemistry remains emerging: researchers still need to improve electrode materials, battery stability, cycle life and overall performance before fluoride-ion systems can compete with established lithium-ion technology.
The work was coordinated by Maurizio Sansotera, with electrochemical characterization led by Luca Magagnin and molecular dynamics research contributed by Giuseppina Raffaini; Federico Maria Scesa was the paper’s lead author. The study appears in the journal Energy Storage Materials.
What Still Stands Between This Membrane and a Working Battery
Is this a finished battery? No. The tests used coin cells with lead and lead fluoride electrodes, which cycled more than 50 times at room temperature — a laboratory demonstration, not a commercial cell.
How much more energy could it hold than lithium-ion? The team cites a theoretical potential of about 600 watt-hours per kilogram for fluoride-ion chemistry, versus approximately 150–250 Wh/kg for standard lithium-ion batteries.
Is the membrane safe? Politecnico di Milano describes the quasi-solid membrane as non-flammable, but the study notes the coin-cell tests do not establish fire safety for a complete battery system.
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