Lithium-ion batteries are the ultimate standard when it comes to mobile phones, electric cars, and tablet devices. Their power density and storage capacity are far greater to other rechargeable battery systems. Regardless of all the progress that has been accomplished, however, smartphone batteries just last for one day and electric cars require hours to be recharged. Researchers are thus looking for ways to enhance the charging rates and power densities of all-round batteries. " An important factor is the anode material," explains Dina Fattakhova-Rohlfing from the Institute of Energy and Climate Research (IEK-1).
Prof. Dina Fattakhova-Rohlfing. (Credit - Forschungszentrum Jülich/Sascha Kreklau)
"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 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.
Prof. Dina Fattakhova-Rohlfing
One method for addressing this issue is hybrid materials or nanocomposites — composite materials that are made up of nanoparticles. The researchers created a material containing tin oxide nanoparticles enhanced with antimony, on a foundation layer of graphene. The graphene basis helps the material’s structural stability and conductivity. The tin oxide particles measure less than 3 nm in size — which translates as less than three-millionths of a millimeter — and are straightaway "grown" on the graphene. The particle’s small size and its good contact with the graphene layer also enhance its tolerance to volume variations — the lithium cell becomes more stable and endures for a longer time.
Three times more energy in one hour
"Enriching the nanoparticles with antimony ensures the material is extremely conductive," explains 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," says Fattakhova-Rohlfing. " 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. W e hope that our development will pave the way for lithium-ion batteries with a significantly increased energy density and very short charging time.
Prof. Dina Fattakhova-Rohlfing