"In principle, anodes based on tin dioxide can achieve much higher specific capacities, and therefore store more energy, than the carbon anodes currently being used. They have the ability to absorb more lithium ions,” says Prof. Fattakhova-Rohlfing. “Pure tin oxide, however, exhibits very weak cycle stability - the storage capability of the batteries steadily decreases and they can only be recharged a few times. The volume of the anode changes with each charging and discharging cycle, which leads to it crumbling."
One way of addressing this problem is hybrid materials or nanocomposites - composite materials that contain nanoparticles. The scientists developed a material comprising tin oxide nanoparticles enriched with antimony, on a base layer of graphene. The graphene basis aids the structural stability and conductivity of the material. The tin oxide particles are less than 3nm in size and are directly ‘grown’ on the graphene. The small size of the particle and its good contact with the graphene layer is said to improve its tolerance to volume changes, meaning the lithium cell becomes more stable and lasts longer.
"Enriching the nanoparticles with antimony ensures the material is extremely conductive," she explains. "This makes the anode much quicker, meaning that it can store one-and-a-half times more energy in just one minute than would be possible with conventional graphite anodes. It can even store three times more energy for the usual charging time of one hour.
"Such high energy densities were only previously achieved with low charging rates. Faster charging cycles always led to a quick reduction in capacity."
The antimony-doped anodes developed by the scientists however, retain 77 % of their original capacity even after 1,000 cycles.
"The nanocomposite anodes can be produced in an easy and cost-effective way. And the applied concepts can also be used for the design of other anode materials for lithium-ion batteries," she adds. "We hope that our development will pave the way for lithium-ion batteries with a significantly increased energy density and very short charging time."
