La han bautizado como batería STAIR (St. Andrew Air), y su aportación se basa en sustituir el electrodo de óxido de litio cobalto con carbono poroso, permitiendo a los iones de litio y a los electrones de la batería reaccionar con el oxígeno.
Normalmente las baterías acarrean todos los compuestos químicos consigo transformando unos en otros y así almacenar carga o liberarla en forma de corriente eléctrica. En este caso se utiliza el oxigeno de la atmósfera de tal modo que no hace falta llevarlo consigo.
Con esta batería se llega a almacenar 4 amperios hora por gramo de carbono. El prototipo culmina con éxito un proyecto de cuatro años de duración que empezó cuando estos investigadores se dieron cuenta que el ciclo de carga-descarga basada en el carbono poroso y el oxígeno atmosférico parecía funcionar bien.
Peter Bruce, uno de los investigadores del proyecto, dice que la clave de todo es el uso del oxígeno atmosférico en lugar de acarrear otros compuestos. El oxígeno debe penetrar a través de un lado de la batería que esté expuesto al aire y reacciona en los poros del carbono para producir electricidad.
El hecho de sustituir materiales tóxicos como el cobalto, níquel y otros elementos, por el carbono, bastante más inocuo, hace que podamos llamar batería “verde” a este invento de los científicos de St Andrews. Si sus pretensiones de comercializar el producto en 5 años se confirman, puede que nos encontremos por fin con el verdadero artífice de la revolución tecnológica del transporte.
A new type of air-fuelled battery could give up to ten times the energy storage of designs currently available
This step-change in capacity could pave the way for a new generation of electric cars, mobile phones and laptops.
The research work, funded by the Engineering and Physical Sciences Research Council (EPSRC), is being led by researchers at the University of St Andrews with partners at Strathclyde and Newcastle.
The new design has the potential to improve the performance of portable electronic products and give a major boost to the renewable energy industry. The batteries will enable a constant electrical output from sources such as wind or solar, which stop generating when the weather changes or night falls.
Improved capacity is thanks to the addition of a component that uses oxygen drawn from the air during discharge, replacing one chemical constituent used in rechargeable batteries today. Not having to carry the chemicals around in the battery offers more energy for the same size battery. Reducing the size and weight of batteries with the necessary charge capacity has been a long-running battle for developers of electric cars.
The STAIR (St Andrews Air) cell should be cheaper than today’s rechargeables too. The new component is made of porous carbon, which is far less expensive than the lithium cobalt oxide it replaces.
This four-year research project, which reaches its halfway mark in July, builds on the discovery at the university that the carbon component’s interaction with air can be repeated, creating a cycle of charge and discharge. Subsequent work has more than tripled the capacity to store charge in the STAIR cell.
Principal investigator on the project, Professor Peter Bruce of the Chemistry Department at the University of St Andrews, says: “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.”
“The key is to use oxygen in the air as a re-agent, rather than carry the necessary chemicals around inside the battery,” says Bruce.
The oxygen, which will be drawn in through a surface of the battery exposed to air, reacts within the pores of the carbon to discharge the battery. “Not only is this part of the process free, the carbon component is much cheaper than current technology,” says Bruce. He estimates that it will be at least five years before the STAIR cell is commercially available.
The project is focused on understanding more about how the chemical reaction of the battery works and investigating how to improve it. The research team is also working towards making a STAIR cell prototype suited, in the first instance, for small applications, such as mobile phones or MP3 players.
The four-year research project “An O2 Electrode for a Rechargeable Lithium Battery” began on 1 July 2007 and is scheduled to end on 30 June 2011. It has received EPSRC funding of £1,579,137.
Rechargeable lithium batteries are currently comprised of a graphite negative electrode, an organic electrolyte and lithium cobalt oxide as the positive electrode. Lithium is removed from the layered intercalation compound (lithium cobalt oxide) on charging and re-inserted on discharge.
Energy storage is limited by the lithium cobalt oxide electrode (0.5 Li/Co, 130 mAhg-1). The University of St Andrews design replaces the lithium cobalt oxide electrode with a porous carbon electrode and allows Li+ and e- in the cell to react with oxygen from the air.
Initial results from the project found a capacity to weight ratio of 1,000 milli-amp / hours per gram of carbon (mA/hours/g), while recent work has obtained results of up to 4,000 mA/hours/g. Although the two designs work very differently, this equates to an eight-fold increase compared to a standard cobalt oxide battery found in a mobile phone.
The application to renewable energy could help get round the problems of intermittent supply. By discharging batteries to provide electricity and recharging them when the wind blows or sun shines, renewables become a much more viable option.
The Engineering and Physical Sciences Research Council (EPSRC) is the UK’s main agency for funding research in engineering and the physical sciences. The EPSRC invests around £740 million a year in research and postgraduate training, to help the nation handle the next generation of technological change. The areas covered range from information technology to structural engineering, and mathematics to materials science. This research forms the basis for future economic development in the UK and improvements for everyone’s health, lifestyle and culture. EPSRC also actively promotes public awareness of science and engineering. EPSRC works alongside other Research Councils with responsibility for other areas of research. The Research Councils work collectively on issues of common concern via Research Councils UK. Website address for more information on EPSRC:
For more information contact:
The University of St Andrews visit: www.st-andrews.ac.uk
Professor Peter Bruce FRS, tel: 01334 463 825, e-mail:firstname.lastname@example.org www.epsrc.ac.uk/PressReleases/oxlithbattery.htm
Rechargeable batteries: Small advances rather than large strides
There’s no ‘silver bullet’ technology on the horizon that will dramatically improve battery life
You can pretty well bank on next year’s new computer being significantly more powerful than this year’s. But if it’s a laptop, that won’t be the case for the rechargeable batteries that run it.
Unlike processors, which tend to double in power every other year, battery power has been doubling about every other decade — and there is some question as to whether even that pace can be maintained.
First, some basics: The rechargeable battery chemistries that have been used in portable devices so far include lithium-ion (li-ion), nickel-metal hydride (NiMH), nickel-cadmium (NiCad) and, if you count cars, lead-acid. Potential battery power, meanwhile, is usually rated in terms of watt-hours per kilogram. Sealed lead-acid batteries can deliver 30 to 50 watt-hours per kilogram, NiCad can deliver 45 to 80, NiMH can deliver 60 to 120, and li-ion can reach as high as 180, according to a site run by Isidor Buchmann, founder and CEO of Cadex Electronics, a maker of battery test equipment and chargers in Vancouver, BC.
Lithium-ion battery performance can improve only a few percentage points per year, most observers agree.
For obvious reasons, therefore, the portable electronics market has largely converted to li-ion chemistry. And given the slow rate of change, li-on is likely to remain the battery of choice for laptops and cell phones for the next three to five years — but things get complicated from there.
Since it was commercialized by Sony in 1991, the power of lithium-ion battery technology "has roughly doubled," Buchmann says. He goes on to explain that, typically, lithium-ion technology has been getting 3% to 4% better per year for the last several years.
This has happened mostly by making the packaging more efficient and by using thinner separators between the layers of reactive materials, explains Ross Dueber, president and CEO of ZPower, a battery startup in Camarillo, Calif.
But, he warns, "Without any move to a new chemistry there will be no dramatic improvements from here."
Buchmann and Dueber agree that thinner separators were the source of the laptop battery fires that have made headlines in the past few years. Numerous recalls were made by Dell and Apple, among other vendors, including the most recent one from Sony in October 2008. The U.S. Consumer Product Safety Commission lists more than a dozen recalls for laptop batteries since 1994 (search under ‘computer equipment’). A li-ion battery fire was also blamed for wrecking a U.S. Navy mini-sub in November 2008. (No one was aboard the sub at the time, and there were no injuries reported.)
Beyond safety, which observers agree has been addressed with stringent quality assurance programs by the manufacturers, li-ion also has a problem with longevity. As anyone who has ever owned a laptop knows, the batteries degrade after repeated charge-discharge cycles.
That, however, may change.
"I believe we are on the onset of a second generation of lithium-ion battery technology," says Christina Lampe-Onnerud, CEO and co-founder of Boston-Power Inc., a li-ion battery startup in Westboro, Mass. The second generation will involve batteries that offer stable levels of power over their usable lives, she indicated. Her company’s second-generation laptop batteries began shipping last December and are being offered by Hewlett-Packard.
The promise of the new batteries is this: If a vendor says the batteries "will power a laptop for four hours, the second generation will deliver consistently four hours," she says. "Maybe that will be four hours 20 minutes at first, and three hours 50 minutes after four years — but not one and a half hours after six months."
She said that the trick is to optimize the battery for how a laptop works. Her firm has invented a new cathode (i.e., the positive electrode — see illustration, below) that uses both manganese and cobalt, an aluminum enclosure instead of stainless steel for better heat dissipation, plus new safety systems, fuses and vents. She added that the new design involves 61 patents.
Buchmann explains that there are actually multiple varieties of li-ion batteries involving cobalt, phosphate or manganese in the reactive material. Cobalt is used in batteries for cell phones and laptops, as it can supply high energy at a steady pace. However, it cannot deliver bursts of power, such as a power tool or car might want. Phosphate and manganese are used in those applications, and offer energy densities as much as a third lower, but there is assumed to be room for improvement there, he notes.
The other rechargeables
NiCad (nickel-cadmium) batteries were the first practical rechargeable battery technology for portable electronics, and are cheaper to make than NiMH (nickel-metal hydride) batteries. But the technology has been largely abandoned due to environmental concerns because of the cadmium they contain, says Norman Deschamps, an analyst for the market research firm SBI in Moncton, New Brunswick. NiCad batteries can still be found in space and telecommunications applications, he notes.
In portable electronics, NiMH batteries are mostly found in inexpensive cordless phones, says ZPower’s Dueber, because NiMH batteries can use cheaper charging and protection circuits than li-ion batteries.
John Petersen, partner with investment firm of Fefer Petersen & Cie in Château de Barberêche, Switzerland,notes that NiMH technology is constrained by the supply of lanthanum, a rare-earth element required to make the batteries, almost all of which currently comes from China. "Otherwise, it’s good technology with solid performance," he says. However, given the lanthanum shortage, he does not expect it to make any additional inroads against li-on in portable electronics.
Meanwhile, "There has been a lot of hype about li-ion in vehicles, but 98 percent of hybrids use NiMH," adds Deschamps. "It is better in terms of the temperature in which it can be charged. All but the newest li-ion batteries can’t be charged below zero degrees Centigrade. That’s not an issue with laptops but it’s a real problem with vehicles. You’ll notice that hybrids are most popular in the Southwest; where the weather is easier on the batteries." NiMH batteries also haven’t started any fires, he added. (For more about car batteries, see this related story.)
Dueber disagrees that battery technology has reached a plateau, as his firm is currently commercializing batteries based on silver-zinc chemistry. He expects to see sales start next year.
"In theory it has about twice the density as lithium-ion, and in practice we are looking at a 40 percent improvement, or about 250 watt-hours per kilogram," he says. The silver is recoverable — it can be melted down and recast in a new battery after the original wears out — as is the zinc, "which is fairly cheap, so we expect recycling to keep the price down," he explains.
He expects retail prices for silver-zinc to be 40% higher than li-ion, or about $1,800 per kilowatt-hour capacity, but he notes that silver and zinc are plentiful compared to lithium, so mass production would not encounter any shortages. Also, the components are not flammable.
"We think there is a lot of runway for improvement with silver-zinc chemistry, much greater than li-ion has in its future, with a theoretical limit of 524 watt-hours per kilogram," Dueber says. There have even been unconfirmed reports of Apple switching to silver-zinc for the battery in its 17-inch MacBook Pro.
The main alternative to batteries is fuel cells — instead of recharging, you add more fuel, which is typically methanol, some form of natural gas, hydrogen, or borohydride (boron and hydrogen).
"The most significant development in the last three years has been the increasing number of commercial sales" of fuel cells, said Robert Wichert, technical director of the US Fuel Cell Council in Washington, DC. Fuel cells are popular with emergency services — in other words, rescue teams that are sent into devastated areas where there is no reliable power supply, and who are likely to stay there longer than would be practical with battery power alone.
Fuel cells are also used for forklifts in enclosed settings where diesel motors would not be acceptable, he says. Also, cell phone towers that formerly relied on diesel generators or lead-acid batteries for backup power have been switching to fuel cells because they take less maintenance and don’t require any start-up time, he added.
A company called MTI MicroFuel Cells has a fuel-cell charger for mobile devices including cell phones and iPods; it provides up to 25 hours of power. And there have been other attempts at fuel cells for mobile phones, including one several years ago by Japan’s two largest mobile communications carriers.
But for computer users, "There are no fuel cell firms claming to have a laptop product," says Michelle Rush, vice president of Medis Technologies, a fuel cell maker in New York. "Most of what you see are larger products," including fuel cells for the data center.
One of Rush’s firm’s products could help on the mobile-computing front. It’s a unit the size of a bar of soap that supplies 20 watt-hours. It’s aimed at recharging the batteries of cell phones and other smaller devices, and she claims it can usually supply 20 hours of power for a smart phone or 60 hours for an MP3 player. The unit, which uses borohydride chemistry, costs $34.99, with refills going for $19.99. Under U.S. Department of Transportation rules, airline passengers are allowed to take three units with them, where they would presumably be used for handheld games on long flights.
A larger unit aimed at laptops is at least 18 months away, she said, adding that she hopes it will cost less than $100.
As for using large capacitors instead of batteries, "They have potential, but more for vehicles than portable electronics," says Deschamps. "Used in conjunction with batteries, they can send out huge bursts of power. But I don’t see any commercial use in the next five years."
Slow but sure progress
While others see looming walls, SBI’s Deschamps believes that every battery chemistry — even lithium ion — ought to be able to show a few percentage points of improvement yearly for the foreseeable future. "A lot of chemistries are available and a lot of things are still not understood at a fundamental level — there is no model that completely describes the chemical interactions. There are only approximations."
Deschamps compares battery development to government bonds. "Growth is slow and steady, but they get there eventually — despite any hype you hear about batteries suddenly getting better," he says.
Petersen also cautions against hype, having heard plenty. "I do think that among investors there are a lot of expectations that there will be the equivalent of Moore’s Law in the battery industry, but that is not going to happen," he says. "You can only get so many electrons out of a given atom.
"Ultimately there will be no one answer," Petersen concludes. "We will end up seeing a lot of different kinds of energy storage for lots of different applications."
Lithium-ion: The next big thing for car batteries?
Costs are high and lithium supplies are not plentiful
Any mention of using lithium-ion in cars triggers negative reactions in some quarters. The current cost for li-ion is about $1,300 per kilowatt-hour capacity. A car such as the upcoming Chevrolet Volt electric hybrid requires a 16,000 kilowatt-hour battery, meaning its battery would cost almost $21,000 — more than many cars.
As for volume production bringing prices down, don’t bet on it, cautions John Petersen, partner with investment firm of Fefer Petersen & Cie in Château de Barberêche, Switzerland. The lithium used in li-ion batteries comes from salt flats in the Andes Mountains of South America, and the supply cannot automatically be expanded to meet higher demand. An aluminum ore available in the U.S., called spodumene contains lithium — but extracting it is expensive since lithium will explode on contact with water, Petersen explains.
Ross Dueber, president and CEO of ZPower, a battery startup in Camarillo, Calif., agrees, saying that 60% to 70% of the cost of a lithium-ion battery is from the cost of the raw materials. "Bolivia is the Saudi Arabia of lithium-ion. The idea that the car industry will be able to bring costs down is optimistic, since we have already done that in the electronics industry. We already have a huge installed base and we already leverage from volume. If we could make it cheaper, we would’ve done so."
The iconic American electric car is the previously mentioned Chevrolet Volt, which should go on the market by the end of calendar 2010, according to General Motors spokesman Brian Corbett. It will use manganese li-ion batteries supplied by a South Korean company, which are expected to last 8 to 10 years, or 150,000 miles. He would not give an expected cost for the batteries because he said the batteries are not to be sold separately — they will be part of the car. (The retail price of the car has also not been announced.)
The use of manganese means the battery can supply bursts of power suitable for a car, and does not impact the price of the battery — around $21,000 — so there is some question about how the Volt can be competitively priced.
Battery management circuitry will prevent both excessive charging and discharging, to prolong battery life, he says.
The vehicle is expected to go 40 miles on a battery charge, and has a small gasoline engine and a generator to extend the range beyond that. Recharging will take three hours at 220 volts and eight hours at 110 volts. A "thermal management system" will prevent the battery from getting too hot or too cold, Corbett explains.
Lead-acid battery technology also continues to improve, says Maurice "Moe" Desmarais, executive vice president of the Battery Council International in Chicago. "Vendors continue to release new products that contain more energy and have longer life spans than previous products, so the technology is improving in all respects. The problem is that you have to do several years of testing — if you are offering a warranty for four years, you need to test it for four years."
Also, the mounds of lead-acid car batteries that used to disfigure junkyards are now gone, and currently recycling rates hover at 99% as the lead in the batteries can be completely reused, Desmarais says. In fact, he notes that municipal garbage workers are generally forbidden to collect car batteries. Currently, car batteries typically last four years but hot weather can decrease their life expectancy, Desmarais says.