Fluoride-ion battery cells pass 50-plus cycles with new non-flammable membrane

Researchers in Italy have developed a polymer membrane that allows fluoride ions to move through a battery electrolyte at room temperature, addressing a major obstacle to the development of next-generation fluoride-ion batteries. The quasi-solid gel membrane, developed by a team at Politecnico di Milano, acts as a fluoride-exchange membrane (FEM), transporting fluoride ions between battery electrodes. The researchers say the approach could help advance an alternative battery chemistry that does not rely on lithium. Fluoride-ion batteries have attracted interest because fluoride is an abundant element and their conversion-based chemistry offers the potential for high energy density. However, developing electrolytes that can transport fluoride ions efficiently at room temperature has remained a significant challenge. The study introduces a polymer electrolyte based on a perfluorosulfonic amide ionomer containing tetraalkylammonium fluoride groups. Membrane enables ion transport To improve the movement of fluoride ions, the researchers modified the polymer membrane using a mixture of two solvents, 1,3-dioxolane (DOL) and dimethyl sulfoxide (DMSO). The solvent mixture causes the ionomer to swell, creating conditions that allow fluoride ions to move through the quasi-solid material. Measurements using electrochemical impedance spectroscopy showed that the membrane achieved ionic conductivity of up to 1.3 millisiemens per centimeter at room temperature. The team also used molecular dynamics simulations to investigate how the membrane’s structure and solvent composition influence fluoride-ion movement. The simulations indicated that DMSO plays an important role as a polar swelling agent. The researchers then tested the electrolyte in experimental coin cells using lead and lead fluoride electrodes. The cells demonstrated reversible fluorination and defluorination, the processes through which fluoride ions move into and out of electrode materials during charging and discharging. The experiments showed stable cycling over more than 50 cycles at room temperature, with a current density of 0.1C. Lithium-free batteries remain distant The researchers describe the membrane as the first fluoride-exchange membrane developed for this type of battery, drawing on the established concepts of proton-exchange and anion-exchange membranes. The university says the quasi-solid membrane is non-flammable, potentially offering a safety advantage for energy storage applications. However, the study’s coin-cell tests do not establish the fire safety or commercial performance of a complete battery system. Fluoride-ion batteries could eventually find applications in stationary energy storage, electric vehicles and aviation. Their theoretical energy density could also exceed that of conventional lithium-ion technologies. The research team cited a potential energy density of around 600 watt-hours per kilogram, compared with approximately 150–250 Wh/kg for standard lithium-ion batteries. Such figures represent potential rather than performance demonstrated by the experimental cells. 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. Despite the progress, fluoride-ion batteries remain an emerging technology. Researchers still need to improve electrode materials, battery stability, cycle life, and overall performance before the chemistry can compete with established lithium-ion systems. The new membrane provides a possible route towards room-temperature fluoride-ion transport, bringing researchers a step closer to practical batteries that use a different charge carrier. The story appears in the journal Energy Storage Materials. Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.