Carbon spheres infused with iron oxide or rust could boost lithium-ion battery energy storage and sustainability, according to a study.

Researchers at Germany’s Saarland University and Austria’s University of Salzburg have collaborated to create a lithium-ion battery electrode that offers a more environmentally friendly alternative to nickel and cobalt.

Their study looks at replacing those materials with iron oxide, the main component of rust, which is cheap, abundant and widely available. 

The Salzburg team created tiny, highly porous, hollow carbon spheres. Known as carbon spherogels, these novel materials – around 250 nanometres in diameter – offer a large surface area that supports high electrochemical capacity.

The Saarland team then introduced finely dispersed iron oxide into these spheres to improve battery performance. Using a scalable synthesis methodology based on iron lactate, they were able to integrate different quantities of iron into the carbon framework of the hollow spheres, producing robust porous networks with evenly distributed iron nanoparticles.

Stefanie Arnold, a postdoctoral researcher at Saarland University, said: “What was particularly interesting was that the storage capacity (i.e. the amount of electric charge that can be reversibly stored and released per gram of active electrode material) continued to increase while the battery was in use. The longer the battery was used, the better it performed. This is because the elemental metallic iron in the nanoparticles first has to react with oxygen to form iron oxide. 

“This process of electrochemical activation of the iron embedded in the carbon spherogel matrix is not immediate but happens progressively. It takes around 300 charge-discharge cycles until all the cavities in the carbon spheres are filled with iron oxide and the maximum storage capacity is reached.”

The researchers say further research is still needed before this mechanism can be used on an industrial scale. The activation process needs to be faster so that batteries can reach their maximum storage capacity sooner. 

In addition, the iron oxide-filled carbon spherogels are currently used as the battery anode; a suitable cathode still needs to be developed to obtain a complete cell.

Professor Volker Presser, professor of energy materials at Saarland University, said: “We are confident that our approach will facilitate the development of environmentally friendly buffer storage systems for renewable energy.”

Since other substances could potentially be incorporated into the spherogels, the researchers plan to test the material in sodium-ion batteries as well.

The study – Iron-loaded carbon spherogels as sustainable electrode materials for high-performance lithium-ion batteries – has been published in the journal Chemistry of Materials.