Engineers at Isentropic Ltd, a company in Cambridge UK, have developed a system fo storing large amounts of energy cheaply using gravel.

Currently, the most economically viable way of storing large amounts of energy is through pumped hydro, in which excess electricity is used to pump water up a hill. The water is held back by a dam until the energy is needed and then released to turn turbines and generate electricity.

Isentopic claims that its gravel-based battery would be able to store equivalent amounts of energy but use less space and be cheaper to set up.

The system consists of two silos filled with gravel. Electricity is used to heat and pressurise argon gas that is fed into one of the silos, heating the gravel to 500°C. When the gas leaves the chamber, it has cooled to ambient temperature but is still pressurised. The pressurised argon is fed into the second silo, where it expands back to normal atmospheric pressure. This process acts like a giant refrigerator, causing the temperature inside the second chamber to drop to -160°C.

In effect, electrical energy is stored as a temperature difference between the two rock-filled silos. To release the energy, the cycle is reversed, and as the energy passes from hot to cold it powers a generator that makes electricity.
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Researchers at the Massachusetts Institute of Technology, led by Associate Professor Yang Shao-Horn, in collaboration with Professor Paula Hammond, have found that using carbon nanotubes for one of the battery’s electrodes produced up to a tenfold increase in the amount of power that a lithiun-ion battery could deliver from a given weight of material.

In the new battery electrode, carbon nanotubes are "electrostatically self-assembled" into a tightly bound structure that is porous at the nanometer scale. The carbon nanotubes have many oxygen groups on their surfaces, which can store a large number of lithium ions. This enables carbon nanotubes to serve as the positive electrode in lithium batteries.

Carbon nanotubes are a form of pure carbon in which sheets of carbon atoms are rolled up into tiny tubes. Normally, carbon nanotubes on a surface tend to clump together in bundles, leaving few exposed surfaces to undergo reactions. The "electrostatic self-assembly" process incorporates organic molecules on the nanotubes and they assemble in a way that has a many exposed surfaces.

The new batteries have some of the advantages of both capacitors and conventional lithium batteries. Like capacitors, they can produce very high power outputs in short bursts - but the energy output for a given weight of the new electrode material is five times greater than for conventional capacitors. Like conventional batteries, they can provide lower power steadily for long periods - but the total power delivery rate with the new batteries is10  times that of lithium-ion batteries

In addition to their high power output, the carbon nanotube electrodes showed very good stability over time. After 1,000 cycles of charging and discharging a test battery, there was no detectable change in the material’s performance.

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Researchers at two institutions have proposed different ways in which the use of ultracapacitors could boost the efficiency and reduce the cost of hybrid vehicles.

According to estimates by researchers at Argonne National Laboratory in Illonois, ultracapacitors could lower the cost of the battery packs in plug-in hybrid vehicles by hundreds, or even thousands of dollars, by halving the size of the packs that are needed.

The cost of the batteries is the main the reason why hybrids cost thousands of dollars more than conventional vehicles. This is especially true of plug-in hybrids, which rely on large battery packs to supply the power during short trips. In addition, batteries degrade over time. To compensate for this, vehicle manufacturers oversize them to ensure that they continue to provide enough power throughout the life of the vehicle.

On the other hand, ultracapacitors, which don’t rely on chemical reactions to store energy, don’t degrade significantly over the life of a car. But they store much less energy than batteries. The Argonne National Laboratory’s proposal is to use both ultracapacitors and batteries. This would protect batteries from intense bursts of power, such as those needed for acceleration, thereby extending the life of the batteries and ensuring that the car could accelerate just as well at the end of its life as at the beginning. Click here to read the rest of this entry.

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Researchers at Ceramatec Inc, a Utah company, have created a small ceramic disk battery which they say will deliver a continuous flow of five kilowatts of electricity over four hours and can be recharged daily for more than ten years.

The new battery runs on sodium-sulphur - a composition that normally operates as a battery at temperatures greater than 300°C. Ceramatec’s new battery runs at less than 90°C. The secret is a thin ceramic membrane that is sandwiched between the sodium and sulfur. Only positive sodium ions can pass through, leaving electrons to create a useful electrical current.

Ceramatec says that batteries will be ready for market testing in 2011, and will sell for about $US2,000.

According to Daniel Nocera, Professor of Energy at the Massachusetts Institute of Technology, who sits on Ceramatec’s advisory board, “These batteries switch the whole dialogue to renewables, They will turn us away from dumb technology, circa 1900 - a 110-year-old approach - and turn us forward.”

Professor Nocera sees the new battery technology as making local power generation and storage, from sources such as solar and wind, practical. He believes that this could take the pressure off the power grid and save tens of billions of dollars needed to upgrade the grid and make it "smart".

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Researchers at the University of Waterloo in Ontario have developed a prototype of a lithium-sulphur rechargeable battery that can store three times the power of a conventional lithium-ion battery in the same volume while being significantly lighter and potentially cheaper to manufacture.

As with lithium-ion technology, lithium-sulphur batteries store the electrical charge in one electrode during the charging phase and release it to the other during the discharge phase. To achieve high performance, sulphur needs to remain in very close contact with a conductor, such as carbon. The research team used mesoporous carbon, a material that has a highly uniform pore structure at the nano-scale, to achieve this. Sulphur was melted and made to fill the tiny voids in the carbon using capillary forces. All the spaces were uniformly filled with sulphur, thus maximizing the surface area in direct contact with carbon and boosting battery efficiency.

According to the leader of the research team, Professor Linda Nazar, the energy density of lithium-sulphur batteries is "about a factor of 3 to 5 times more than a conventional lithium-ion battery" while the raw materials are cheaper.

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Researchers in the UK are developing a rechargeable lithium-air battery that could deliver a ten-fold increase in energy capacity compared to that of currently available lithium-ion cells. The research at the University of St Andrews, with partners at Strathclyde and Newcastle, is funded by the Engineering and Physical Sciences Research Council,

Lithium-air batteries use a catalytic air cathode in combination with an electrolyte and a lithium anode. Oxygen from the air is the active material for the cathode and is reduced at the cathode surface.

According to Professor Peter Bruce of the Chemistry Department at the University of St Andrews, "The key is to use oxygen in the air as a re-agent, rather than carry the necessary chemicals around inside the battery. Our target is to get a five to ten fold increase in storage capacity, which is beyond the horizon of current lithium batteries. Our results so far are very encouraging and have far exceeded our expectations."

Professor Bruce estimates that it will be at least five years before the batteries are commercially available.

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MIT materials scientists Byoungwoo Kang & Gerbrand Ceder have published a paper in Nature describing a new battery technology which allows for ultrafast charging and discharging of lithium-ion batteries.  The discovery could lead to cellphone-sized batteries that could be charged in 10 seconds.

"The ability to charge and discharge batteries in a matter of seconds rather than hours may open up new technological applications and induce lifestyle changes," they wrote.

In energy storage, there has always been a trade-off between the amount of energy a material could store and how quickly you could charge and discharge it. Batteries are good at storing energy but getting the energy into and out of them is more difficult. The new battery material solves the problem by applying a special surface coating to the lithium iron phosphate which creates a "fast-lane" for ions to move around the material. This allows the ions to speed around the battery resulting in recharging 100 times more quickly than with current lithium-ion batteries.

Although batteries are notoriously difficult to scale out of the laboratory into production, the scientists believe that the new technology could make it to the market in two to three years. The technology has already been licensed by two manufacturers.

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