How To Charge Lithium Batteries 20 Times Faster

A touch of asphalt may be the secret to high-capacity lithium metal batteries that charge 10 to 20 times faster than commercial lithium-ion batteries, according to Rice University scientists. The Rice lab of chemist James Tour developed anodes comprising porous carbon made from asphalt that showed exceptional stability after more than 500 charge-discharge cycles. A high-current density of 20 milliamps per square centimeter demonstrated the material’s promise for use in rapid charge and discharge devices that require high-power density.

Scanning electron microscope images show an anode of asphalt, graphene nanoribbons and lithium at left and the same material without lithium at right. The material was developed at Rice University and shows promise for high-capacity lithium batteries that charge 20 times faster than commercial lithium-ion batteries

The capacity of these batteries is enormous, but what is equally remarkable is that we can bring them from zero charge to full charge in five minutes, rather than the typical two hours or more needed with other batteries,” Tour said.

The Tour lab previously used a derivative of asphalt — specifically, untreated gilsonite, the same type used for the battery — to capture greenhouse gases from natural gas. This time, the researchers mixed asphalt with conductive graphene nanoribbons and coated the composite with lithium metal through electrochemical deposition. The lab combined the anode with a sulfurized-carbon cathode to make full batteries for testing. The batteries showed a high-power density of 1,322 watts per kilogram and high-energy density of 943 watt-hours per kilogram.

Testing revealed another significant benefit: The carbon mitigated the formation of lithium dendrites. These mossy deposits invade a battery’s electrolyte. If they extend far enough, they short-circuit the anode and cathode and can cause the battery to fail, catch fire or explode. But the asphalt-derived carbon prevents any dendrite formation.

The finding is reported in the American Chemical Society journal ACS Nano.

Source: http://news.rice.edu/

Graphene Nanoribbons Boost Electronics

Graphene, an atom-thick material with extraordinary properties, is a promising candidate for the next generation of dramatically faster, more energy-efficient electronics. However, scientists have struggled to fabricate the material into ultra-narrow strips, called nanoribbons, that could enable the use of graphene in high-performance semiconductor electronics.

Now, University of Wisconsin-Madison engineers have discovered a way to grow graphene nanoribbons with desirable semiconducting properties directly on a conventional germanium semiconductor wafer. This advance could allow manufacturers to easily use graphene nanoribbons in hybrid integrated circuits, which promise to significantly boost the performance of next-generation electronic devices. The technology could also have specific uses in industrial and military applications, such as sensors that detect specific chemical and biological species and photonic devices that manipulate light.

In a paper published Aug. 10 in the journal Nature Communications, Michael Arnold, an associate professor of materials science and engineering at UW-Madison, Ph.D. student Robert Jacobberger, and their collaborators describe their new approach to producing graphene nanoribbons. Importantly, their technique can easily be scaled for mass production and is compatible with the prevailing infrastructure used in semiconductor processing.

graphene nanoribbonsProgressively zoomed-in images of graphene nanoribbons grown on germanium. The ribbons automatically align perpendicularly and naturally grow in what is known as the armchair edge configuration.

 

 

Graphene nanoribbons that can be grown directly on the surface of a semiconductor like germanium are more compatible with planar processing that’s used in the semiconductor industry, and so there would be less of a barrier to integrating these really excellent materials into electronics in the future,” Arnold says.

Source: http://news.wisc.edu/

New Cheap Catalyst For Hydrogen Electric Car

Graphene nanoribbons formed into a three-dimensional aerogel and enhanced with boron and nitrogen are excellent catalysts for fuel cells, used in hydrogen electric car, even in comparison to platinum, according to Rice University researchers. The reactions in most current fuel cells are catalyzed by platinum, but platinum’s high cost has prompted the search for alternative. A team led by materials scientist Pulickel Ajayan and chemist James Tour made metal-free aerogels from graphene nanoribbons and various levels of boron and nitrogen to test their electrochemical properties. In tests involving half of the catalytic reaction that takes place in fuel cells, they discovered versions with about 10 percent boron and nitrogen were efficient in catalyzing what’s known as an oxygen reduction reaction, a step in producing energy from feedstocks like methanol.
Ajayan’s Rice lab has excelled in turning nanostructures into macroscopic materials, like the oil-absorbing sponges invented in 2012 or, more recently, solid nanotube blocks with controllable densities and porosities.

hydrogen-electric car
The key to developing carbon-based catalysts is in the doping process, especially with elements such as nitrogen and boron,” he said. “The graphitic carbon-boron-nitrogen systems have thrown many surprises in recent years, especially as a viable alternative to platinum-based catalysts.”. The Rice process is unique, he said, because it not only exposes the edges but also provides porous conduits that allow reactants to permeate the material.
The research appeared in the American Chemical Society journal Chemistry of Materials.

Source: http://news.rice.edu/