"An important factor is the anode material," said Prof Dina Fattakhova-Rohlfing from the Institute of Energy and Climate Research (IEK-1) in Juelich near Cologne who led the research. "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. 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."
The graphene base of the nanocomposite aids the structural stability and conductivity of the material. The 3nm tin oxide particles are grown directly on the graphene and the small size of the particle and its good contact with the graphene layer also improves its tolerance to volume changes - the lithium cell becomes more stable and lasts longer.
"Enriching the nanoparticles with antimony ensures the material is extremely conductive," said Fattakhova-Rohlfing. "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," she said. "Faster charging cycles always led to a quick reduction in capacity." In contrast, the antimony-doped anodes retain 77 percent of their original capacity even after 1,000 cycles.