By introducing finely dispersed iron oxide into tiny, highly porous hollow carbon spheres—developed by Professor Michael Elsaesser at the University of Salzburg—the Saarbrücken team has achieved very promising results.
These results represent increased storage capacities using readily available materials that are far less problematic from an environmental standpoint. The findings have been published in the journal Chemistry of Materials.
Anyone who has ever been to Salzburg, Austria, knows about Mozartkugeln, the famous chocolate balls filled with marzipan and nougat. These sweet treats help to imagine the hollow carbon spheres developed by researchers at the University of Salzburg and now being used at Saarland University to advance lithium-ion battery technology. Known as carbon spherogels, these new materials consist of nanometric units about 250 nm in diameter, offering a large surface area and high electrochemical capacity
“Our challenge is to use chemical synthesis to fill the inner cavity of these spheres with suitable metal oxides,” explains materials scientist Stefanie Arnold. After initial experiments with titanium dioxide, whose ability to store and release lithium ions proved relatively low, the team turned its attention to iron oxide, commonly known as rust.
“Iron has several advantages: it is abundant worldwide, offers—at least in theory—a high storage capacity, and is easy to recycle,” says Arnold, a postdoctoral researcher at Saarland University working with Professor Volker Presser, Chair of Energetic Materials. Using a scalable synthesis method based on iron lactate, the Salzburg team succeeded in integrating varying amounts of iron into the carbon structure of hollow spheres, generating robust porous networks with uniformly distributed iron nanoparticles.
“What was particularly interesting was that the storage capacity—that is, the amount of electrical charge that can be reversibly stored and released per gram of active electrode material—continued to increase while the battery was in use. The more the battery was used, the better it performed,” Arnold explains. This is because the elemental metallic iron in the nanoparticles must first react with oxygen to form iron oxide. This electrochemical activation process is not immediate but gradual. It takes about 300 charge-discharge cycles for all the cavities in the carbon spheres to fill with iron oxide and reach maximum storage capacity.
“Oxide-based batteries” are still under development.
However, further research is required before this mechanism can be applied on an industrial scale. The activation process needs to be accelerated so that the batteries reach their maximum capacity in less time. Furthermore, carbon spherogels filled with iron oxide are currently used as the anode; a suitable cathode still needs to be developed to obtain a complete cell.
“We are confident that our approach will facilitate the development of environmentally friendly intermediate storage systems for renewable energies,” says Volker Presser, who also heads the Energy Materials Research Department at INM – Leibniz Institute for New Materials in Saarbrücken. The new material will also be tested in sodium-ion batteries, which are already being used by Chinese car manufacturers. “These materials constitute a versatile technological platform that allows a wide variety of substances to be integrated into the spherogels in a single synthesis step, opening up opportunities for numerous technological applications,” adds Michael Elsaesser.
New recycling methods and a more sustainable energy supply.
As part of the EnFoSaar project, Stefanie Arnold is also investigating how to recover lithium from batteries and how future batteries should be designed to be disassembled on an industrial scale. “We need efficient recycling methods and closed-loop material systems to minimize resource consumption and reduce waste in the battery supply chain,” says Arnold.
EnFoSaar is a major project funded by the Saarland State Government with €23 million from the Saarland Transformation Fund. Its aim is to develop innovative approaches to climate-friendly energy supply and promote the transformation of the regional energy industry and associated scientific landscape through innovative, scientifically sound, and practically applicable methodologies.
Original publication:
Iron-Loaded Carbon Spherogels as Sustainable Electrode Materials for High-Performance Lithium-Ion Batteries
Authors: Saeed Borhani, Le Thi Thao, Gregor A. Zickler, Antje Quade, Michael S. Elsaesser, Volker Presser, Stefanie Arnold
