Batteries can be charged
times faster with the new composite material than those with a conventional graphite anode
Whether mobile phone or electric car – when it comes to energy on the go, lithium-ion batteries are currently the measure of all things. They are far superior to other batteries regarding memory capacity and power density. If only they loaded faster and lasted longer! Despite all progress, smartphone batteries often run flat after one day, and electric cars take hours to recharge.
A team of researchers from Jülich, Munich and Prague have come an important step closer to better batteries. The materials researchers produced a new composite material for electrodes, which could not only significantly increase the storage capacity and service life but also the charging speed of lithium batteries. A battery equipped with it could store three times as much energy in an hour’s charging time as would be possible with conventional graphite anodes. The scientists published their results in the journal “Advanced Functional Materials”.
When it comes to higher energy densities and charging rates, the anode material is an important factor. “Anodes based on tin dioxide can in principle store much more energy than the carbon anodes that are currently used, as they have the ability to absorb more lithium ions,” explains Prof. Dina Fattakhova-Rohlfing of the Institute of Energy and Climate Research. However, this is purchased at a disadvantage, reports the chemist: “Pure tin oxide shows very poor cycle stability – the storage capacity of the batteries decreases steadily and they can only be recharged a few times. The volume of the anode changes with each charging and discharging cycle, which causes it to crumble.”
To counter this problem, the researchers combined tin oxide with other materials to form nanocomposites – composite materials containing nanoparticles. The scientists developed a material consisting of tin oxide nanoparticles enriched with antimony on a graphene base. Graphene is a single layer of carbon atoms that are arranged like a honeycomb. It stabilises the structure while contributing to conductivity. The tin oxide particles are less than three nanometers (or millionths of a millimeter) in size and are “grown” directly onto the graphene. Due to the small size of the particles and their good contact with the graphene layer, the tolerance to changes in volume is improved – the lithium cell remains stable for a longer time.
The antimony nanoparticles are responsible for the rapid charging of the batteries. “Enriching the nanoparticles with antimony makes the material extremely conductive,” explains Fattakhova-Rohlfing. “It makes the anode much faster.”
Previously, such high energy densities could only be achieved if the batteries were charged slowly. Faster charging cycles always led to a rapid reduction in capacity. The antimony-doped anodes, on the other hand, still retain 77 per cent of their original capacity even after 1,000 cycles.
In addition, they can be produced easily and cheaply, explains Fattakhova-Rohlfing, and the concepts can also be used for other anode materials. “We hope that our development will pave the way for lithium-ion batteries with a significantly higher energy density and a very short charging time.”
PHOTOS: Forschungszentrum Jülich/Sascha Kreklau