North Carolina State Improves Lithium-Ion Batteries and Stacked Solar Cells

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Researchers at North Carolina State University have been busy. One research group created a new flexible nano-scaffold for rechargeable lithium ion batteries that could help make cell phone and electric car batteries last longer. NC State researchers have also developed a new technique for improving the connections between stacked solar cells, which should improve the overall efficiency of solar energy devices and reduce the cost of solar energy production.

The battery research, published online in Advanced Materials, shows the potential of manufactured sheets of aligned carbon nanotubes coated with silicon, a material with a much higher energy storage capacity than the graphite composites typically used in lithium ion batteries.

 “Putting silicon into batteries can produce a huge increase in capacity—10 times greater,” said Dr. Philip Bradford, assistant professor of textile engineering, chemistry and science at NC State. “But adding silicon can also create 10 times the problems.”

One significant challenge in using silicon is that it swells as lithium ion batteries discharge. As the batteries cycle, silicon can break off from the electrode and float around (known as pulverization) instead of staying in place, making batteries less stable.

When the silicon-coated carbon nanotubes were aligned in one direction like a layer of drinking straws laid end to end, the structure allowed for controlled expansion so that the silicon is less prone to pulverization, said Xiangwu Zhang, associate professor of textile engineering, chemistry and science at NC State.

“There’s a huge demand for batteries for cell phones and electric vehicles, which need higher energy capacity for longer driving distances between charges,” Zhang said. “We believe this carbon nanotube scaffolding potentially has the ability to change the industry, although technical aspects will have to be worked out. The manufacturing process we’re using is scalable and could work well in commercial production.”

The research was supported by the Donors to the American Chemical Society Petroleum Research Fund.

 

Stacked Solar Cells Connection

Another North Carolina State research group discovered a way for solar cell manufacturers to stack solar cells so they can handle high-intensity solar energies without losing voltage at the connecting junctions, potentially improving conversion efficiency. The new connections can allow these cells to operate at solar concentrations of 70,000 suns worth of energy without losing much voltage as “wasted energy” or heat.

Stacked solar cells consist of several solar cells that are stacked on top of one another. Stacked cells are currently the most efficient cells on the market, converting up to 45 percent of the solar energy they absorb into electricity.

But to be effective, solar cell designers need to ensure the connecting junctions between these stacked cells do not absorb any of the solar energy and do not siphon off the voltage the cells produce – effectively wasting that energy as heat.

“We have discovered that by inserting a very thin film of gallium arsenide into the connecting junction of stacked cells we can virtually eliminate voltage loss without blocking any of the solar energy,” says Dr. Salah Bedair, a professor of electrical engineering at NC State and senior author of a paper describing the work.

This work is important because photovoltaic energy companies are interested in using lenses to concentrate solar energy, from one sun (no lens) to 4,000 suns or more. But if the solar energy is significantly intensified – to 700 suns or more – the connecting junctions used in existing stacked cells begin losing voltage. And the more intense the solar energy, the more voltage those junctions lose – thereby reducing the conversion efficiency.

“Now we have created a connecting junction that loses almost no voltage, even when the stacked solar cell is exposed to 70,000 suns of solar energy,” Bedair says. “And that is more than sufficient for practical purposes, since concentrating lenses are unlikely to create more than 4,000 or 5,000 suns worth of energy. This discovery means that solar cell manufacturers can now create stacked cells that can handle these high-intensity solar energies without losing voltage at the connecting junctions, thus potentially improving conversion efficiency.

“This should reduce overall costs for the energy industry because, rather than creating large, expensive solar cells, you can use much smaller cells that produce just as much electricity by absorbing intensified solar energy from concentrating lenses. And concentrating lenses are relatively inexpensive,” Bedair says.

 

 

Discuss this Blog Entry 3

on Nov 16, 2013

Electric cars are very much efficient and also Eco-friendly. These are known as Green cars. These are the future of car industry. Electric cars are not smokey and also better for the environment. These are the charged cars and charging of the battery is very importance in case of an Electric car. Now a day, Charging stations are available everywhere and it is too easy to charge the Electric car whenever require. Electric Car Repair also very necessary for the better performance of the car.

on Dec 8, 2013

Spot on with this write-up, I seriously think this site needs a lot more attention. I’ll probably be returning to read more, thanks for the advice! insanity workout free

on Jun 18, 2014

Good information about the battery make and its use, in the electric car, battery use more than the other so how can use the battery in a proper way for the long running is important. Battery can used as per the engine capacity and what type of electricity needed for a vehicle. There are variety type of battery available with different volts and size, for the electric car, battery charging requirement is higher than the other.
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