Proof-of-concept anodes built with graphene nanoribbons (GNRs) and tin oxide showed an initial capacity better than the theoretical capacity of tin oxide alone, according to Rice chemist James Tour.
After 50 charge-discharge cycles, the test units retained a capacity that was still more than double that of the graphite currently used for LI battery anodes.
Graphene is the single atom-thick form of carbon, the discovery of which won a Nobel Prize in 2010 because of its potentially transformative effects in electronics, solar energy and battery technology. Scientists believe it could pave the way for a host of innovations including windows that act as computer displays and super-light aerospace components.
The Rice researchers have developed a method to make graphene nanoribbons in bulk and are moving toward commercial applications. One area for improvement is the battery because in an increasingly mobile world battery capacity is becoming a bottleneck that generally limits devices to less than a day’s worth of use.
In the new experiments, the Rice lab mixed graphene nanoribbons and tin oxide particles about 10nm wide in a slurry with a cellulose gum binder and water, then spread it on a current collector and encased it in a button-style battery. The GNRs not only separate and support the tin oxide but also help deliver lithium ions to the nanoparticles.
Lab tests showed initial charge capacities of more than 1,520 milliamp hours per gram (mAh/g). Over repeated charge-discharge cycles, the material settled into a solid 825mAh/g.
‘It took about two months to go through 50 cycles,’ said lead author Jian Lin, a postdoctoral researcher at Rice, who believes it could handle many more without losing significant capacity.
GNRs could also help overcome a prime difficulty with LI battery development as lithium ions tend to expand the material they inhabit, and the material contracts when they’re pulled away. Over time, materials like silicon, which shows extraordinary capacity for lithium, break down and lose their ability to store ions.
Other labs at Rice are said to have made breakthroughs that help solve the expansion problem by breaking treated silicon into a powder, achieving great capacity and many cycles. GNRs take a different approach by giving batteries a degree of flexibility, Tour said.
‘Graphene nanoribbons make a terrific framework that keeps the tin oxide nanoparticles dispersed and keeps them from fragmenting during cycling,’ he said in a statement. ‘Since the tin oxide particles are only a few nanometres in size and permitted to remain that way by being dispersed on GNR surfaces, the volume changes in the nanoparticles are not dramatic. GNRs also provide a lightweight, conductive framework, with their high aspect ratios and extreme thinness.’
The researchers pointed out the work is a starting point for exploring the composites made from GNRs and other transition metal oxides for lithium storage applications. Lin said the lab plans to build batteries with other metallic nanoparticles to test their cycling and storage capacities.
Other recent research at Rice found that pairing graphene nanoribbons with vanadium could also enhance battery performance.
The research appeared this week in the American Chemical Society journal ACS Nano.
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