Super-Charging Lithium Batteries

Nanowire electrodes could improve the performance of electric vehicles.

Existing lithium batteries can enable battery-powered electrical vehicles to travel hundreds of miles on a charge, prompting a race among major automakers to demonstrate that the batteries are safe and durable enough for mass marketing. Battery developers, meanwhile, continue to push lithium performance. Last month, Stanford University materials scientists unveiled a nanowire electrode that could more than triple lithium batteries' energy storage capacity and improve their safety.

Swelling nanowires: Upon charging with lithium ions, these silicon nanowires swell from 89 nanometers wide (top) to 141 nanometers wide and elongate (bottom); they can accommodate 10 times more lithium ions than conventional graphite electrodes can. As a result, the nanowires could more than triple the energy capacity of lithium batteries.


Credit: Yi Cui

The development, reported in the scientific journal Nature Materials, stems from the labs of nanowire innovator Yi Cui and battery expert Robert Huggins at Stanford's Materials Science and Engineering Department. The researchers show that nanowires of silicon just a few atoms across can function as high-capacity electrodes, absorbing and releasing about 10 times more lithium ions than the graphite electrodes that are commonly used today.

Charging a lithium battery usually means moving lithium ions from the battery's positive electrode or cathode into its negative electrode or anode. Silicon has the right electrochemical affinity for lithium ions to make it a promising material for anodes. In fact, until now, it has been a bit too promising. Silicon anodes absorb too much lithium. Upon charging, the silicon anodes swell to four times their previous volume, fracturing the material. After just a few charging cycles, the anodes are finished.

Nanowires, in contrast, take the swelling in stride. The Stanford collaborators' silicon nanowires swell when charged from 89 nanometers wide to 141 nanometers wide and simultaneously elongate, thereby releasing the strain. They show no signs of mechanical failure after more than 20 cycles.

Nor, according to Cui, do the silicon nanowires appear as susceptible as graphite to typical failure mechanisms that cause safety problems (including fires that prompted new rules from the U.S. Department of Transportation this week limiting lithium batteries in checked luggage). "Potentially, silicon is going to be much safer than carbon," says Cui, who points out that improved safety could be key to lithium's future acceptance in vehicles. "It only takes an accident or two to destroy a technology." He says that testing over many more cycles is under way to confirm the silicon-nanowire anode's enhanced durability and safety.

The downside is that the nanowire growth process that Cui uses, which feeds gaseous silicon to a liquid gold catalyst to make the solid electrode, is a high-temperature (600 to 900 °C) process that could be costly to scale up. Cui believes that scale-up of the vapor-liquid-solid process is nevertheless feasible, but he acknowledges that he is also "exploring another approach."

Ohio State University chemist Yiying Wu, who also works on nanowire electrodes, calls the Stanford work "definitely very important." But Wu and other materials scientists caution that additional advances will be required before lithium batteries with nanowire electrodes deliver major increases in performance of electric-vehicle batteries. Not least is the need to scale up the process of making nanowires, which have yet to be mass-produced for commercial application.

Another limitation is that while Cui's silicon nanowires make great anodes, lithium-battery technology has greater need for improved cathodes. In a given battery, substituting an anode that stores more lithium ions has no impact without a corresponding cathode that can supply more charge.

Both Cui and Wu (who reported his own lithium anode development last month with a high-capacity cobalt-oxide nanowire) say that their labs are working on novel materials for cathodes. "That's the holy grail for this business," says Wu. "Anyone who can generate much higher cathode capacity will bring a huge breakthrough for the lithium battery."

Biofuel Bonanza

The energy bill signed this week will have an enormous impact on biofuels.

Friday, December 21, 2007

By David Rotman

In case you were a bit busy this week and didn't have time to examine the 822 pages of the Energy Independence and Security Act of 2007, it is a big deal. And in particular, it is a big deal for biofuels.

The numbers speak for themselves. The legislation, which was signed by President Bush on Wednesday, creates an enormously ambitious Renewable Fuel Standard (RFS) that mandates the production of 36 billion gallons of renewable fuels by 2022; included in that is 21 billion gallons of advanced biofuels (most of which will be cellulosic biofuels). At such levels, biofuels will account for more than 20 percent of total road-transportation fuels in the United States by 2022. To give a sense of the ambition of such a mandate, it is worth noting that total biofuel production in 2007 was only 4.7 billion gallons, and almost all of that was corn-derived ethanol. There is still no commercial production of cellulosic ethanol.

The biofuel industry is, of course, thrilled. Bio, the biotechnology trade association that counts among its members numerous companies involved in various aspects of biofuels, predicts that the new mandates will mean nearly 300 new biofuel plants, including 75 new corn ethanol plants and 210 new cellulosic ethanol plants. Bio estimates that the RFS could mean $170 billion invested in advanced technology development, biofuel production, and new infrastructure to handle biofuels.

Overall, the federal mandate for biofuels appears to be a good thing. It will finally give industry and academic researchers confidence that biofuels are really going to play an important role in the country's energy future. But it is worth keeping in mind that there are still huge technology challenges in ramping up production of advanced biofuels. Achieving the ambitious standards of the new energy law will require an equally ambitious effort in researching and developing advanced biofuel technologies.

The Price of Biofuels

Do we really have any alternative to biofuels?

Superbugs
Since the oil crisis of the 1970s, when the price of a barrel of petroleum peaked, chemical and biological engineers have chased after ways to turn the nation's vast reserves of "cellulosic" material such as wood, agricultural residues, and perennial grasses into ethanol and other biofuels. Last year, citing another of President Bush's goals--reducing U.S. gasoline consumption by 20 percent in 10 years--the U.S. Department of Energy (DOE) announced up to $385 million in funding for six "biorefinery" projects that will use various technologies to produce ethanol from biomass ranging from wood chips to switchgrass.

According to a 2005 report by the DOE and the U.S. Department of Agriculture, the country has enough available forest and agricultural land to produce 1.3 billion tons of biomass that could go toward biofuels. Beyond providing a vast supply of cheap feedstock, cellulosic biomass could greatly increase the energy and environmental benefits of biofuels. It takes far less energy to grow cellulosic materials than to grow corn, and portions of the biomass can be used to help power the production process. (The sugarcane-based ethanol produced in Brazil also offers improvements over corn-based ethanol, thanks to the crop's large yields and high sugar content.)

But despite years of research and recent investment in scaling up production processes, no commercial facility yet makes cellulosic ethanol. The economic explanation is simple: it costs far too much to build such a facility. Cellulose, a long-chain polysaccharide that makes up much of the mass of woody plants and crop residues such as cornstalks, is difficult--and thus expensive--to break down.

Several technologies for producing cellulosic ethanol do exist. The cellulose can be heated at high pressure in the presence of oxygen to form synthesis gas, a mixture of carbon monoxide and hydrogen that is readily turned into ethanol and other fuels. Alternatively, industrial enzymes can break the cellulose down into sugars. The sugars then feed fermentation reactors in which microörganisms produce ethanol. But all these processes are still far too expensive to use commercially.

Even advocates of cellulosic ethanol put the capital costs of constructing a manufacturing plant at more than twice those for a corn-based facility, and other estimates range from three times the cost to five. "You can make cellulosic ethanol today, but at a price that is far from perfect," says Christopher Somerville, a plant biologist at the University of California, Berkeley, who studies how cellulose is formed and used in the cell walls of plants.

"Cellulose has physical and chemical properties that make it difficult to access and difficult to break down," explains Caltech's Arnold, who has worked on and off on the biological approach to producing cellulosic ethanol since the 1970s. For one thing, cellulose fibers are held together by a substance called lignin, which is "a bit like asphalt," Arnold says. Once the lignin is removed, the cellulose can be broken down by enzymes, but they are expensive, and existing enzymes are not ideal for the task.

Many researchers believe that the most promising way to make cellulosic biofuels economically competitive involves the creation--or the discovery--of "superbugs," microörganisms that can break down cellulose to sugars and then ferment those sugars into ethanol. The idea is to take what is now a multistep process requiring the addition of costly enzymes and turn it into a simple, one-step process, referred to in the industry as consolidated bioprocessing. According to Lee Lynd, a professor of engineering at Dartmouth College and cofounder of Mascoma, a company based in Cambridge, MA, that is commercializing a version of the technology, the consolidated approach could eventually produce ethanol at 70 cents a gallon. "It would be a transformational breakthrough," he says. "There's no doubt it would be attractive."

But finding superbugs has proved difficult. For decades, scientists have known of bacteria that can degrade cellulose and also produce some ethanol. Yet none can do the job quickly and efficiently enough to be useful for large-scale manufacturing.

Nature, Arnold explains, offers little help. "There are some organisms that break down cellulose," she says, "but the problem is that they don't make fuels, so that doesn't do you much good." An alternative, she says, is to genetically modify E. coli and yeast so that they secrete enzymes that degrade cellulose. But while many different kinds of enzymes could do the job, "most them don't like to be inserted into E. coli and yeast."

Arnold, however, is optimistic that the right organism will be discovered. "You never know what will happen tomorrow," she says, "whether it's done using synthetic biology or someone just scrapes one off the bottom of their shoe."

She didn't quite scrape it off her shoe, but Susan Leschine, a microbiologist at the University of Massachusetts, Amherst, believes she just might have stumbled on a bug that will do the job. She found it in a soil sample collected more than a decade ago from the woods surrounding the Quabbin Reservoir, about 15 miles from her lab. The Quabbin sample was just one of many from around the world that Leschine was studying, so it was several years before she finished analyzing it. But when she did, she realized that one of its bacteria, Clostridium phytofermentans, had extraordinary properties. "It decomposes nearly all the components of the plant, and it forms ethanol as the main product," she says. "It produces prodigious amounts of ethanol."

Leschine founded a company in Amherst, ­SunEthanol, that will attempt to scale up ethanol production using the bacterium. There's "a long way to go," she acknowledges, but she adds that "what we have is very different, and that gives us a leg up. We already have a microbe and have demonstrated it on real feedstocks." Leschine says that other useful microbes are probably waiting to be discovered: a single soil sample, after all, contains hundred of thousands of varieties. "In this zoo of microbes," she says, "we can think that there are others with similar properties out there."

Blooming Prairies
Whether ethanol made from cellulosic biomass is good or bad for the environment, however, depends on what kind of biomass it is and how it is grown.

In his office in St. Paul, David Tilman, a professor of ecology at the University of Minnesota, pulls out a large aerial photo of a field sectioned into a neat grid. Even from the camera's vantage point far above the ground, the land looks poor. In one plot are thin rows of grasses, the sandy soil visible beneath. Tilman says the land was so infertile that agricultural use of it had been abandoned. Then he and his colleagues scraped off any remaining topsoil. "No farmer has land this bad," he says.

In a series of tests, Tilman grew a mixture of native prairie grasses (including switchgrass) in some of the field's plots and single species in others. The results show that a diverse mix of grasses, even grown in extremely infertile soil, "could be a valuable source of biofuels," he says. "You could make more ethanol from an acre [of the mixed grasses] than you could from an acre of corn." Better yet, in a paper published in Science, Tilman showed that the prairie grasses could be used to make ethanol that is "carbon negative": the grasses might consume and store more carbon dioxide than is released by producing and burning the fuel made from them.

The findings are striking because they suggest an environmentally beneficial way to produce massive amounts of biofuels without competing with food crops. By 2050, according to Tilman, the world will need a billion hectares more land for food. "That's the land mass of the entire United States just to feed the world," he says. "If you did a lot of biofuels on [arable] land--it is very easy to envision a billion hectares for biofuels--you will have no nature left and no reserve of land after 50 years." Instead, ­Tilman argues, it makes sense to grow biomass for fuels on relatively infertile land no longer used for agriculture.

But down the hill from Tilman's office, his colleagues in the applied-economics department worry about the practical issues involved in using large amounts of biomass to make fuel. For one thing, they point out, the technology and infrastructure that could efficiently handle and transport the bulky biomass still need to be developed. And since the plant material will be expensive to move around, biofuel production facilities will have to be built close to the sources of feedstock--probably within 50 miles.

The amount of biomass needed to feed even one medium-size ethanol facility is daunting. Eidman calculates that a facility producing 50 million gallons per year would require a truck loaded with biomass to arrive every six minutes around the clock. What's more, he says, the feedstock is "not free": it will cost around $60 to $70 a ton, or about 75 cents per gallon of ethanol. "That's where a lot of people get fooled," he adds.

Since no commercial cellulosic facility has been built, says ­Eidman, it is difficult to analyze the specific costs of various technologies. Overall, he suggests, the economics look "interesting"--but cellulosic ethanol will have to compete with corn-derived biofuels and get down to something like $1.50 a gallon. Eidman believes it will be at least 2015 before biofuels made from cellulose "are much of a factor" in the market.

Advanced Technologies Group SkyCat Hybrid Air Vehicle, United Kingdom

The SkyCat hybrid air vehicles, supplied by Advanced Technologies Group, based in Cardington, Bedfordshire, UK, combine lighter-than-air airship technology and air-cushioned hovercraft technology. The vehicle will be built in three variants, the Skycat 20, 200 and 1000 with payload capacities from 20,000kg to 1,000,000kg. The first SkyCat will be the SkyCat 20 for which the first flight is anticipated in 2006.

In July 2005, the Advanced Technologies Group Ltd went into administration under Part II of the Insolvency Act 1986. The future of the development programme of the SkyCat is thus uncertain.

The air cushion landing system allows the vehicle to land on flat land, grass, swamp, snow or on water, giving the vehicle fully amphibious capability. The landing system also allows the airship to land without the normal lighter-than-air airship ground crew and ground landing infrastructure.

The SkyCat can be configured as a passenger airship, an ultra heavy cargo ship and as an airborne surveillance platform. Military applications include tactical and strategic air lift, a command, control, computers and information platform, mine countermeasures, airborne early warning and anti-surface warfare.

SKYCAT DESIGN

The SkyCat layout includes an advanced lifting body, an ellipsoidal-shaped cross section hull and a catamaran-hover-cushion system. The development of the SkyCat is based on the proven successful design, manufacture and operation of the fleet of airships by Airship Technologies, which designs and operates more transport and passenger airships than any other airship operator worldwide. The maximum operating altitude is 2,745m.

The envelope structure incorporates a laminated fabric envelope. The envelope is a large bag containing the lighter-than-air helium gas which provides the airship with much of its lift. Helium is an inert gas which is not flammable. The payload module is built on the centre line of the airship. An internal catenary structure supports the payload. The envelope shape is supported by an internal configuration of diaphragms, which can be used to compartmentalise the structure.

The SkyCat has a patented ATG bow-thruster that allows the direction of the nose to be accurately controlled at low speeds, dispensing with the need for large numbers of ground crew.

SKYCAT 1000

The largest variant of the vehicle, the SkyCat 1000, has a maximum payload capacity of one million kg, which is nearly ten times the capacity of a Boeing 747-200 freighter aircraft. The cruise speed of the SkyCat 1000 is 185km/h, which is a fifth of the speed of the 747. The range is 7,408km compared to the 747's 8,700km range.

The first flight of the SkyCat 1000 is scheduled for 2008. The mission of the SkyCat 1000 as an ultra heavy lift air vehicle has been assessed by the United States Army in a study initiated in 2001.

The main cargo deck provides 195m² (2,100ft²) of clear loading space. The deck is fitted with a military load rated floor. The area above the door aperture provides an additional 195m² floor area and a number of mezzanine floors can be installed to provide additional deck area. Roll on/roll off ramps are installed in the fore and aft of the airship allowing fast and efficient embarkation / disembarkation to the cargo area.

SKYCAT 20

The main cabin of the SkyCat 20 is 22.3m long by 3m wide and is fitted with four passenger seats The cabin has a large side door with integral steps and a full width rear cargo door.

The SkyCat 20 carries a maximum payload of 20,000kg. The cruise and maximum speeds are 130km/h and 148km/h respectively. The maximum payload range is 2,250km. The ferry range is over 7,400km.

The SkyCat 20 development program was completed in 1999 and manufacture was started in 2000. SkyCat 20 will enter service with World Airships (UK) in 2005/2006.

SKYCAT 200

The SkyCat 200 cabin is 49.4m long by 7.5m wide and is equipped with a rear roll on/roll off ramp. There is space for an additional 37m² of floor area above the door aperture.

SkyCat 200 carries a maximum payload of 200,000kg, about 80% more than a 747 freighter payload. The cruise speed is 139km/h and the range is 5,970km.

SKYCAT FLIGHT DECK

The flight deck accommodates two pilot stations which are fitted with conventional stick controls. The pilots have an exceptionally wide and deep field of view through the large transparent windows. The flight deck can also accommodate off duty flight and cabin crew or training crew members with 18.6m² of floor space available on the SkyCat 200 and 83.6m² floor space in the SkyCat 1000.

The dual-channelled optically signalled flight control system is based on fibre-optic technology or "fly-by-light" to send signals to the powered control actuators.

SKYCAT LANDING SYSTEM

The air cushion landing system is derived from hovercraft technology with hoverskirts installed on the underside of the outer hull section. The hover skirts are held flat against the hull by the air pressure which gives the hull an aerodynamic profile during flight and also allows an all round view from the cabin. The hover skirt and the hull pressure system are operated by the ballonet fans.

ENGINES

The SkyCat 20 is powered by four ATG A-Tech 600 direct injection diesel engines rated at 447kW. The larger SkyCat 200 is equipped with four 5,996kW turboshaft engines. The engines are installed in ducts with two engines on the forward hull and two engines on the rear hull. Blown vanes in the ducts provide the vector thrust for take-off, and landing and for manoeuvring on the ground.

The SkyCat 1000 is powered by six turboshaft engines, each rated at 11,185kW. One engine is installed on each side of the forward hull. Two engines are installed in the stern duct on each side of the hull with each engine driving a single propeller.

The ship is equipped with a 28V DC electrical power system and a low pressure pneumatic system. The pneumatic system powers the flight control actuators. The pneumatic system provides very low susceptibility to lightening strike.

The SkyCat hybrid air vehicles combine lighter-than-air airship technology with air-cushioned hovercraft technology.

The vehicle will be built in three variants (Skycat 20, SkyCat 200 and SkyCat 1000) with payload capacities from 20,000kg to one million kg.

Four views of the SkyCat 20, showing the double-hull shape which provides lift from the aerodynamic design and from the helium inside.

The remotely controlled Sky Kitten prototype, which is 13m long.

SkyCat 20 could be used for roles including firefighting.

SkyCat can hover on station for extended periods, making it ideal for loading/unloading cargo at sea.

Insane Rides: Aeroscraft Hybrid Airship

Airships, or dirigibles, have been around at least since the late 1700s, though they've never quite caught on as a mainstream form of transportation. In fact, zeppelins, which are technically "rigid" airships, are better known for their famous namesakes than anything else (the doomed German vessel Hindenburg, for example, or even the band Led Zeppelin!).

As more sophisticated aircraft came to prominence in the mid-20th century, airships fell out of favor. But they do continue to find useful applications even today, and some aircraft companies have big plans for this particular type of vessel as we move into the 21st century. The Aeroscraft hybrid airship, for example, isn't your granddad's idea of a zeppelin at all, though it certainly qualifies as an Insane Ride…
Aeroscraft Hybrid Airship

- Worldwide Aeros

Type of Vehicle: Hybrid airship

Production Status: Non-rigid prototype (Aeros 40D) flight testing planned for 2008; full-scale ML866 in production for 2010 launch

Function: Private air yacht; fully functional airborne business center; sightseeing cruise vessel; cargo transport; advertising billboard for the Off-World Colonies and "the chance to begin again in a golden land of opportunity and adventure"

Maximum Range: 3,100 miles

Under the Hood: While airships tend to be used mostly for advertising purposes these days, Worldwide Aeros, the makers of the Aeroscraft, foresee a much wider range of applications for craft of this type. The vessel will be heavier than air -- which by definition means it's not a true airship -- that will utilize helium for part of its buoyancy but will also use six turbofan jet engines for vertical takeoff and landing. Aft propellers will provide forward thrust when at cruising altitude, and the vessel's aerodynamic shape will also help provide lift once the craft is airborne (thanks to the company's Dynamic Buoyancy Management system, a new technology). The Aeroscraft will be able to hit a top speed of 138 mph but its cruising speed will be around 115 mph. The maximum operating altitude will be 12,000 feet, and it will able to reach a range of about 3000 miles (roughly the length of the U.S.). Unlike existing airships, the Aeroscraft will be capable of carrying large payloads of cargo and/or hundreds of passengers, and it will not be confined to airports or airfields for landing and takeoff. The craft could be used as a private yacht for the wealthy, a cruise ship for the rest of us, a military transport, or -- if and when the time comes -- a great safe house and headquarters for hiding out up in the clouds during a zombie plague down on terra firma.

Chances of Owning One: If you're a member of Led Zeppelin, you could no doubt afford one of these zeppelin-like rides yourself when they debut. If not, then you're probably looking at riding it as a passenger. Check Orbitz or Expedia in a couple of years.