A new polymer electrolyte to replace lithium ions in batteries. It's the result of a research carried out by a team from the Department of Chemistry, Materials and Chemical Engineering (DCMIC) "Giulio Natta" at Politecnico di Milano, which conceived and developed a revolutionary, non-flammable, quasi-solid gel membrane that enables the transport of fluoride ions within batteries at room temperature.
The study, published in the prestigious journal Energy Storage Materials, is the outcome of a collaboration between several professors and laboratories within DCMIC, thanks to an interdisciplinary approach that brought together different expertise in chemistry, materials engineering, electrochemistry and molecular dynamics. The key researchers involved were the coordinator Maurizio Sansotera, head of the Fluoritech laboratory; Luca Magagnin, head of the SEE Lab – Surface Engineering and Electrochemistry Laboratory, who was responsible for the electrochemical characterization; and Giuseppina Raffaini, whose contribution in molecular dynamics was fundamental to understanding the mechanisms underlying fluoride ion transport through the polymer membrane.
The study is pioneering precisely because it defines, for the first time, the concept of a Fluoride Exchange Membrane (FEM), by analogy with the widely used proton exchange membranes (PEMs), already employed in numerous applications, and anion exchange membranes (AEMs).
The advantages of fluoride-ion batteries are multiple and relevant, starting with their environmental impact, as they could make use of materials that are more readily available and far more abundant than lithium. Moreover, they could play an active role in the energy transition, in energy storage systems needed to store energy generated from renewable sources, thanks to a fundamental characteristic of this innovative material: its non-flammability. "Renewable energy sources have production peaks that occur at times that do not coincide with peak consumption. To address this problem, several European countries are developing storage systems for the energy produced, but the widespread adoption of these systems is often limited by concerns about the fire risk associated with batteries," explains Maurizio Sansotera, Professor of Fundamentals of Chemistry. "The technology we are developing is based on the use of a non-flammable polymer membrane that reduces the risk of fire, while also offering the advantage of using an element that is abundant and evenly distributed in nature."
Not only safer, but also lighter batteries capable of lasting longer, as they could offer higher theoretical energy densities. "We are talking about approximately 600 watt-hours per kilogram, compared with around 150–250 for standard lithium-ion batteries. In practice, this would mean roughly twice the battery life: an electric car could travel twice as many kilometres," says Luca Magagnin, Professor of Applied Physical Chemistry. "There are many possible applications, from energy storage systems to drones, satellites and aircraft."
Another fundamental aspect is that fluoride ion transport in the polymer electrolyte developed takes place at room temperature. "The quasi-solid membrane we have designed enables fluoride ion transport at room temperature. This makes it possible to avoid wasting the energy required to preheat the battery," emphasizes Giuseppina Raffaini, Professor of Chemistry and Materials. "In previous generations of fluoride-ion batteries, by contrast, operating temperatures of around 100–150 degrees were required to improve ionic conductivity, consuming part of the stored energy by dissipating it as heat."
The fluoride-ion gel membrane also makes it possible to overcome dependence on lithium and represents an important step forward towards the development of next-generation batteries, with the prospect of offering higher energy density, greater safety and improved sustainability.
