Graphene Packs a Solar Punch & New Batteries Hold More than their Own

Recent technological discoveries can lead to wider adoption of renewable solar energy. One is the discovery that properties of graphene are unaffected by application of thin silicon film, which can lead to thinner and more efficient solar panels. Another is the discovery of the use of lithium-sulfur in making longer lasting batteries capable of holding bigger charges, which can ensure continued energy supply even when the sun is not shining. Pictured is lithium-air battery with graphene bubbles, lighter in weight than current batteries. Which means less weight, less cost and more energy which sounds like the future to us. Read More

Graphene solar cells now one step closer to reality

By CleanTechnica on (14 October 2013):

Graphene solar cells are now one step closer to reality, thanks to a new discovery made by researchers at the HZB Institute for Silicon Photovoltaics. The discovery: the many impressive properties of graphene, such as extreme conductivity and “complete” transparency for example, are apparently completely unaffected by the application of thin silicon film. The discovery means that thin-film photovoltaics which utilize graphene’s many great qualities could be just off the horizon.

Graphene is considered by many researchers to be a “near perfect” candidate material for the transparent contact layers used in solar cells — thanks to the material’s ability “to conduct electricity, without reducing the amount of incoming light.” That’s what’s been theorized anyway — until the material is tested in real-world environments, there are unknowns. This new research now brings the day when graphene can be be tested for this purpose, in real-world conditions, that much closer.

Graphene was deposited onto a glass substrate. The ultrathin layer is but one atomic layer thick (0.3 Angström, or 0.03 nanometers), although charge carriers are able to move about freely within this layer. This property is retained even if the graphene layer is covered with amorphous or polycrystalline silicon.

“We examined how graphene’s conductive properties change if it is incorporated into a stack of layers similar to a silicon based thin film solar cell and were surprised to find that these properties actually change very little,” explains researcher Marc Gluba.

The press release from the Helmholtz-Zentrum Berlin für Materialien und Energie provides details on the research:

To this end, they grew graphene on a thin copper sheet, next transferred it to a glass substrate, and finally coated it with a thin film of silicon. They examined two different versions that are commonly used in conventional silicon thin-film technologies: one sample contained an amorphous silicon layer, in which the silicon atoms are in a disordered state similar to a hardened molten glas; the other sample contained poly-crystalline silicon to help them observe the effects of a standard crystallization process on graphene’s properties.

Even though the morphology of the top layer changed completely as a result of being heated to a temperature of several hundred degrees C, the graphene is still detectable.

“That’s something we didn’t expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon,” states researcher Norbert Nickel. “Measurements of carrier mobility using the Hall-effect showed that the mobility of charge carriers within the embedded graphene layer is roughly 30 times greater than that of conventional zinc oxide based contact layers.”

Gluba adds: “Admittedly, it’s been a real challenge connecting this thin contact layer, which is but one atomic layer thick, to external contacts. We’re still having to work on that.”

Source: www.reneweconomy.com.au

Chinese scientist may have discovered the future of batteries

Chris Davis in China Daily/Asia News Network (15 October 2013):

Ford Motor Co and the University of Michigan just announced they would open a new $88 million battery research and manufacturing lab that they hope will accelerate a much-needed breakthrough for the stalling electric auto non-boom (electric cars accounted for less than 1 per cent of US auto sales last year; hybrids 3 per cent, according to the AP). And batteries are getting the blame.

One of the first persons they should talk to is Chengdu Liang, a staff scientist at Oak Ridge National Laboratory in Tennessee who was born and raised in Hunan province and came to the US about 15 years ago as a graduate student at the University of Tennessee- Knoxville, did a year of post-grad at Oak Ridge and stayed on there, becoming a staff scientist in 2006.

Since then his research has focused on the development of sustainable energy technologies. “Electrical energy storage is a very important and exciting area,” he told China Daily recently, mentioning that China Daily was his favourite newspaper through his college years in Hunan.

“A sustainable energy future lies in the harvesting of intermittent renewable energies to a stable supply of electricity,” he explained, in other words, “When the sun is not shining and the wind is not blowing, the supply of energy is drawing from massive storage of electricity.”

And that means batteries, big batteries. “Large scale storage of electricity needs advanced battery systems that are safe, low cost, and high energy-density,” Liang said.

This past summer, Liang and his team announced a major breakthrough that could have major implications for the quest for an ideal battery for electric cars, not to mention homes and hand-helds.

The secret lies in sulfur, as in lithium-sulfur. The most widely accepted technology for batteries today is lithium-ion, which is practical for consumer electronics but not for anything much bigger. “Large-scale energy storage like vehicles or the electricity grid – if you want to store energy from a solar panel or from a wind turbine – we cannot store it in a lithium-ion battery,” Liang said. “It’s too expensive.”

With today’s electric cars, he said, “one third of the price goes to the battery. If you had a vehicle and the gas tank cost one-third of the price, you would not buy that vehicle”. Same goes for a battery, he said, which is really just an energy “tank”.

Liang and his team had a hunch that sulfur held the answer.People had been working with using sulfur as an electrolyte for years, but always dissolved in a liquid that bridged the anode and cathode, or positive and negative terminals. Liang and his team reworked the entire structure of the battery, discovered some new compounds for the elctrodes, but the major innovation was to use sulfur in its solid form.

Putting it all together, they discovered what Liang calls “the magic” of what he believes “is going to be the future of the next generation of batteries”.

“Our approach is a complete change from the current battery concept of two electrodes joined by a liquid electrolyte, which has been used over the last 150 to 200 years,” Liang said in an Oak Ridge release.

Judged by weight and density, the lithium-sulfur technology outperforms today’s conventional lithium-ion four to one.

Lithium-sulfur is also promising because the cost is so low. “It’s almost free – sulfur is an industry waste,” Liang said. “And the lithium itself is not expensive either.”

“Not only does sulfur store much more energy,” Liang said, “but a lithium-sulfur device could help recycle a waste product into a useful technology.”

Another advantage of the technology is that it does away with the need for flammable liquid electrolytes, which have caused fires on airliners recently.

And if that is not enough, the all-solid sulfur-based battery offers a solution to another problem: self-discharge. As Liang explains, when you charge up a battery and put it on the shelf, after a certain amount of time, it goes dead. In conventional electric car batteries with liquid electrolytes, you charge up your battery, drive to the airport, park and go on vacation for a week or two and come back, “unfortunately, because of self-discharge, you have to call AA”.

Liang said that so far his team has noticed no self-discharge from their design.

The new battery is still in the testing “demo” stage and a patent is pending. As for when lithium-sulfur power packs will be available to cars and cell phones, he said “we still need some improvements and engineering work … we are scientists. We are working on the very fundamental research. We solve the scientific problem then give the engineers a chance to play with that.

“What we work out is the scientific problem,” he said, and “the science question has been answered”.

Liang says that Oak Ridge National Laboratory is “a very nice place to work. I really like the scientific environment here, everything is open, we have collaborations all over the world, anyone can come here to do research.”

The folks at Ford and Michigan might do well to take note.

Source: www.usa.chinadaily.com.cn