Gregoire's CleanTech Blog

Higher-Capacity Lithium-Ion Batteries

Nanostructured electrodes and active materials could shrink batteries for portable electronics and electric vehicles.

A forest of copper rods about 100 nanometers in diameter create much more surface area for high-capacity battery electrodes.

Researchers in France have created lithium-ion battery electrodes with several times the energy capacity, by weight and volume, of conventional electrodes. The new electrodes could help shrink the size of cell-phone and laptop batteries, or else increase the length of time a device could run on a charge. What's more, the nanotech methods used to make these electrodes could provide a simple and inexpensive way to structure new materials for next-generation batteries for plug-in hybrid and all-electric vehicles.

The key advance is the development of an inexpensive and simple way to organize tiny particles into a desired nanostructure, says Patrice Simon, a chemistry professor at the Université Paul Sabatier, who participated in the work along with other researchers at the university and Université Picardie Jules Verne.

In a conventional battery electrode, ions and electrons will move quickly into and out of the active material -- allowing fast charging and discharging -- only if the material is deposited in a very thin film. Thin films, however, limit the amount of active material that can be incorporated into a battery. For high-capacity batteries, engineers typically increase the thickness of the active material, trading off fast charging and high-power bursts for more energy storage.

This new nanostructure allows for both high power and high storage capacity. Active materials are applied in a very thin film to copper nanorods anchored to sheets of copper foil. This thin film allows for fast movement of ions and electrons -- providing the power. At the same time, the high surface area of the forest of nanorods makes it possible to pack much more active material into an electrode than thin films typically allow, thus increasing energy capacity. The rods provide 50 square centimeters of surface area for every square centimeter of electrode.

In addition, the high ion and electron mobility of the thin layer makes it possible to use a new active material and a new chemical reaction for lithium-ion batteries. This new chemistry is attractive because it can accommodate far more lithium ions, and their electron counterparts, than the chemistry used now, thereby potentially storing more energy.

The new electrodes, which would be used as the negative electrodes in lithium-ion batteries, also showed the ability to retain their high capacity after being charged and discharged many times, suggesting that the electrodes may have a long useable lifetime, Simon says, although more extensive tests are needed to confirm this supposition.

Because this advance, described online this week in Nature Materials, applies so far to negative electrodes, the percentage increase in capacity over today's batteries will depend on the capacity of the positive electrode as well. (See "Battery Breakthrough" for a description of one possible positive electrode candidate cited by the researchers.) The first applications of the technology will likely be extremely small batteries, Simon says. These could be useful for remote sensors or medical implants. Further applications will require increasing the size of the electrodes that the researchers can make, and also optimizing the active material they use.

The materials used in reported experiments are not energy efficient -- about 20-25 percent of the energy used to charge them cannot be recovered while discharging them. This energy loss is not a big problem with cell-phone batteries, says Gerbrand Ceder, materials science and engineering professor at MIT. "Over the lifetime you probably spend a few pennies in charging the cell phone," he says. But for larger energy applications, such as electric vehicles, this lack of efficiency could be costly, especially with high electricity prices. For this reason, the researchers are incorporating different high-capacity active materials into their nanostructured electrodes that do not have this energy efficiency problem.

In turning to nanotechnology to improve batteries, the French researchers are not unique. At least two companies, A123 Systems, in Watertown, MA, and Altair Nano, in Reno, NV, have made batteries that include electrodes with nanostructured active materials; and numerous research groups around the world are developing such electrodes. Simon describes his group's process as being simpler and cheaper than many other methods for making nanostructures. It is also versatile, capable of being used with a variety of active materials, he says.

It could also be important for another key trend in battery research: the move away from flat layers of electrode materials to positive and negative electrodes that interpenetrate -- a three-dimensional architecture that can improve the mobility of ions and electrodes, thereby increasing battery power. The French group is also now working on a three-dimensional battery, says Simon, that will combine their negative electrodes with a high-performance positive electrode.

By Kevin Bullis

Source : Technology Review

Battery Breakthrough -- An Update

As President Bush talks up the need for more research, scientists are making advances in hybrids and all-electric vehicles.

While President Bush spoke this week about a new kind of highly efficient hybrid vehicle, on a visit to battery-maker Johnson Controls in Milwaukee, WI, an article appeared in the current issue of Science describing the latest in a series of recent advances that could make hybrids, and even all-electric vehicles, practical.

Researchers have long known that a material based on lithium, nickel, and manganese could be used to make lithium-ion batteries that store large amounts of energy. The problem has been that batteries based on this material could be charged and discharged only slowly, otherwise the amount of energy they could store would drop dramatically.

In the Science paper, researchers at MIT and the State University of New York (SUNY) in Stony Brook described a way around the problem. The breakthrough came last summer, when Kisuk Kang, a materials science graduate student at MIT, created a computer model that showed that when it was under conditions of high power, disorder in the lithium-nickel-manganese material caused it to compress and trap the lithium ions that allow electricity to flow. The researchers then synthesized a version of this material without this disorder, freeing the ions to move quickly.

The newly structured material might be a candidate for replacing the batteries used in today's hybrids cars. But its real value could come in taking advantage of both its power and high energy storage capacity in a different kind of hybrid, known as a plug-in hybrid -- the potentially highly-efficient vehicle Bush spotlighted in his speech on Monday, saying these cars could eventually get

100 miles

per gallon. The new technology could also help make all-electric vehicles practical.

President Bush came to Johnson Controls, which last fall announced a new center of excellence for developing lithium-ion batteries for hybrids, to talk up his Advanced Energy Initiative, first announced in this year's State of the Union address. The Bush administration's 2007 budget provides $31 million for battery technology research, compared with $150 million for research into deriving ethanol from biomass, and nearly twice that amount, $288 million, for hydrogen fuel-cell research.

Unlike today's hybrids, which ultimately depend on gasoline for power, but run efficiently by storing extra energy in batteries, a plug-in hybrid would use energy from the outlet in a garage, charging overnight, and would run completely on electricity for distances typical in a daily commute. The gasoline-powered engine would only kick in for long trips, after the batteries were depleted. This type of hybrid could save significant amounts of gasoline, since something like 75 percent of daily driving is for short trips, says Gerbrand Ceder, the materials science professor at MIT who led the effort to develop the new material.

Ceder says the new material could reduce the weight of battery packs for plug-in hybrids by four to five times. The higher rate capability should also make for speedier charging, allowing top-offs between trips that extend the distance a vehicle could go between overnight recharges.

Other attractive features of batteries based on the new material, according to Ceder, are improved safety over other lithium-ion batteries and lower cost. Lower cost, lighter weight, and faster charging might make the batteries attractive for electric vehicles as well.

The material still needs to go through extensive testing to find out if it will have the longevity and performance capability needed for demanding automotive applications, says Khalil Amine, group leader for battery research at Argonne National Laboratory.

The MIT-SUNY research joins other recent advances in battery materials. Amine's own work at Argonne has produced promising new lithium-ion electrodes, as has that of researchers at A123 Systems in Watertown, MA, and E-One Moli Energy in British Columbia. Meanwhile, Firefly Energy, Peoria, IL, is developing lighter lead-acid batteries that may work well for hybrids.

Developing battery packs using these new technologies and incorporating them into hybrids could take several years, as automakers perform further tests and integrate the technologies into their vehicle development cycles. Even then, the impact on fuel prices and energy consumption could take decades, as consumers gradually purchase the more efficient vehicles.

Because of this long time frame, some experts, including John Heywood at MIT, say that, to achieve shorter-term reductions in oil consumption and prices, people will have to buy cars available now that have better fuel economy. "The only things that work really fast are for people to change their buying and driving habits," Heywood says. To encourage these changes, advocates have called for higher fuel-economy standards and tax breaks for purchasing higher fuel-economy vehicles.

Meanwhile, the MIT-SUNY computer model could help the field generally. Stanley Whittingham, professor of chemistry at SUNY, whose work led to the first commercialized lithium-ion batteries (and who was not involved with the current project), says the computer model, by showing how disorder affects materials, will help other researchers to develop new high-performance batteries. As for the new material, "In the end, to really determine whether this is a critical material, what we need is some extended cycling," he says. "But the rate capability looks great. It looks really promising."

By Kevin Bullis

Source : Technology Review

The Ultra Battery : A new type of ultracapacitor could eventually have you throwing out your conventional batteries.

A breakthrough technology is holding forth the promise of charging electronic gadgets in minutes, never having to replace a battery again, and dropping the cost of hybrid cars. Indeed, the technology has the potential to provide an energy storage device ten times more powerful than even the latest batteries in hybrid cars -- while outliving the vehicle itself.

The new technology, developed at MIT's Laboratory for Electromagnetic and Electronic Systems, should improve ultracapacitors, by swapping in carbon nanotubes, thereby greatly increasing the surface area of electrodes and the ability to store energy.

Ultracapacitors, a souped-up version of the capacitors widely used in electronics, have been around for decades. They're well-known for being powerful, that is, able to quickly absorb and release electricity. But they can't store much energy, so their stored electricity is depleted in a matter of seconds. As a result, they've been limited to niche applications, such as providing quick bursts of power in some hybrid transit buses.

Now researchers at MIT have found what they believe is a way to improve the endurance of ultracapacitors several-fold -- allowing the devices to retain the power and longevity advantages, while storing about as much energy as the batteries used in hybrids.

The amount of energy ultracapacitors can hold is related to the surface area and conductivity of their electrodes. The researchers have increased surface area by "more than an order of magnitude" by using carbon nanotubes, says Joel Schindall, professor of electrical engineering at MIT and one of the researchers on the project. One square centimeter of conductive plate, when coated with the nanotubes, has a surface area of about 50,000 square centimeters, compared with 2,000 square centimeters using the carbon in a commercial ultracapacitor today. The highly pure carbon nanotubes are also extremely conductive, which should increase power output over existing ultracapacitors, the researchers say.

The technology may find applications beyond hybrids, too. Ultracapacitors could allow laptops and cell phones to be charged in a minute. And, unlike laptop batteries, which start losing their ability to hold a charge after a year or two, they could still be going strong long after the device is obsolete. "Theoretically, there's no process that would cause the [ultracapacitor] to need to be replaced," says professor John Kassakian, another of the researchers.

The main hurdle the new technology is likely to face is not technical but economic. "The nanomaterials are probably a hundred or a thousand times more expensive, today, than the materials that we use," says Michael Sund, spokesperson at Maxwell Technologies, San Diego, CA, a maker of commercial ultracapacitors. "The markets that we serve are price-enabled. If our product stored a hundred times more energy, but cost a hundred times more, there might not be any market for it."

However, the MIT researchers hope that, over time, and with help from economies of scale, nanotube ultracapacitors can be made for the same cost as batteries.

The next step is to measure the performance of a device using the carbon nanotubes and to grow the nanomaterials on a flexible substrate that can be rolled into a large-scale ultracapacitor.

By Kevin Bullis