Prof. Dina Fattakhova-Rohlfing. (Image: FZ Juelich)
Graphene has been earmarked for energy storage applications for years. The fact that graphene is just surface area is very appealing to battery applications in which anodes and electrodes store energy in the material that covers them.
With lithium ion (Li-ion) batteries representing the most ubiquitous battery technology, with uses ranging from our smart phones to electric cars, increasing their storage capacity and shortening their charging times with graphene has been a big research push.
Unfortunately, the prospects for graphene in energy storage have been stalled for years. This is in part due to the fact that while graphene is all surface area, in order to get anywhere near the kind of storage capacity of today’s activated carbon you need to layer graphene. The result after enough layering is you end up back with graphite, defeating the purpose of using graphene in the first place.
Now a team of German researchers has developed an approach for improving the anodes of Li-ion batteries that uses graphene in support of tin oxide nanoparticles.
"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," said Dian Fattakhova-Rohlfing, a researcher at Forschungszentrum Jülich research institute in Germain, in a press release. "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 research described in the Wiley journal Advanced Functional Materials, uses graphene as a base layer in a hybrid nanocomposite in which the tin oxide nanoparticles enriched with antimony are layered on top of the graphene. The graphene provides structural stability to the nanocomposite material.
The combination of the tin oxide nanoparticle being enriched with antimony makes them extremely conductive, according to 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."
The scientists found that in contrast to most batteries the high energy density did not have to come with very slow charging rates. Anybody who has a smartphone knows how long it takes to charge it to 100 percent.
"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."
In contrast, the research found that their antimony-doped anodes retain 77 percent of their original capacity even after 1,000 cycles.
Because tin oxide is abundant and cheap, the scientists claim that the nanocomposite anodes can be produced in an easy and cost-effective way.
Fattakhova-Rohlfing added: "We hope that our development will pave the way for lithium-ion batteries with a significantly increased energy density and very short charging time."