JUL 16, 2014 12:00 AM PDT

Battery Technology Charges Ahead

WRITTEN BY: Peter Micheli
It's a common sight. People everywhere in public places such as airports and malls are looking for places to recharge their phones or computers. Cell phones, laptops, electric cars, cameras. All of these would be improved with a better energy storage device. Batteries have improved greatly, but their basic concept hasn't changed much since it was developed by Alessandro Volta over 100 years ago.

The go-to storage device for mobile devices is the lithium-ion battery. Over five billion are sold a year. Today's lithium-ion batteries hold twice as much energy and are ten times cheaper than the first commercial ones that debuted in 1991. But, researchers think we are close to getting as much out of them as we are going to get. It's believed that further improvements can get in up to 30% more energy by weight, which is not enough to give an electric car the range of a gasoline-powered car or to power a heavily used smartphone for many days.

Now there are efforts to move beyond lithium-ion technology. The U.S. Joint Center for Energy Storage Research (JCESR), a partnership of five national laboratories, five universities, and four private-sector organizations has been granted $120 million by the U.S. Department of Energy to meet a very aggressive goal --- to develop storage systems with five times the energy density of today's systems, at one-fifth the cost within five years. . Other research groups in Asia, Europe, and the Americas are also trying to find the replacement for lithium ion technology. Battery researcher Jeff Dahn of Dalhousie University in Halifax, Nova Scotia calls the goal "impossible," but believes aiming for this target will focus efforts on the most promising technologies.

One technology that holds promise is based on a lithium-sulfur design. In theory such a battery can hold five times the energy by weight than lithium -ion but scientists think in reality it may be closer to only twice as much. Lithium-sulfur batteries were first considered about 40 years ago but could only be drawn down and recharged about 100 times. However, recent versions of lithium-sulfur batteries have been shown to go through this cycle 1,500 times while only losing half of their capacity. This performance is similar to that of lithium-ion batteries, but lithium-sulfur would have a weight and cost advantage. Still, there are many technical problems to work out. Some scientists think that problems that don't appear in research settings will rear their ugly heads when the batteries are made for commercial conditions.

Another technology being looked at is the magnesium-ion battery. Using magnesium instead of lithium could double the energy carried per volume, but unlike lithium which rushes through electrolytes and electrodes, magnesium, with its two charges moves as if through molasses. For commercial use researchers must develop new electrolytes with improved properties.

Lithium-oxygen batteries that pull in oxygen from the air are being eyed for use in electric vehicles. They could have a huge weight advantage over other batteries and in theory store energy as densely as a gasoline-powered engine, but they have many technical challenges to overcome, not the least of which is their poor performance in the presence of moisture. In an interview with Design News, Elton Cairns, professor of chemical and biomolecular engineering at the University of California, said, "You have to somehow access the oxygen in the air without allowing in any water. And that's a very, very tough task."

Although lithium-oxygen batteries could solve the range-limiting energy density problem for electric cars, Winfried Wilcke, head of IBM's nanoscience and technology division believes the real thing that's holding back the acceptance of electric vehicles is price, not range. He believes that a sodium-oxygen battery could be the answer. Since sodium is cheaper than lithium it could get the cost of battery packs down to the $100-kWh range, as opposed to today's $500 kWh range. But, development of sodium-oxygen technology is in its very early stages.

Despite major obstacles, the JCESR presses on with its mission. Dahn says, "It's early days: people are looking at really oddball systems, and everyone's trying to figure out how to get the lifetime up and the costs down. The JCESR for one, is hoping that basic research can fill in the gaps and make these technologies work." George Crabtree, director of the JCESR says, "The beyond-lithium-ion space is rich with opportunity and mostly unexplored."
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