Manufactured sulphur cathode allows up to 500 cycles
An inexpensive class of battery—which combines industrial waste product and plastic, and a storage capacity comparable to batteries used in portable computers—is said to be capable of hundreds of cycles without losing function.
Researchers from the National Institute of Standards and Technology (NIST), the University of Arizona in Tucson and Seoul National University in Korea have developed a slimmer version of lithium-ion, the lithium-sulphur (Li-S). These batteries' cathodes are made mainly of sulphur, a cheap waste product of petroleum processing.
The new battery's performance would be competitive in today's marketplace, said NIST materials scientist Christopher Soles. "Five hundred cycles with the capacity we've shown is definitely better than what is in your laptop today."
Batteries deliver power by shuttling positive ions between two electrodes—an anode and a cathode—while electrons travel around a circuit and do useful work. In the past decade, compact batteries using tiny lithium ions have achieved ever larger energy densities, packing more power in smaller volumes and helping to make smart phones and other mobile technologies ubiquitous. But lithium-ion batteries require bulky cathodes, typically made from ceramic oxides like cobalt oxide, to house the ions, which limits the battery's energy density. This means that for more power-intensive applications like long-range electric vehicles, even lithium-ion technology does not cut it.
Sulphur, often an industrial waste product, could be key to future high-performance batteries. Source: E-Fotolia
Sulphur weighs barely half as much as cobalt, atom for atom, and can pack more than twice as many lithium ions into a given volume as can cobalt oxide. Li-S batteries thus have several times the energy density of lithium-ion batteries.
Sulphur cathodes, however, have two major weaknesses. Sulphur easily combines with lithium to form compounds that crystallise and gum up the battery's insides, resulting in a tendency to crack under the stress of repeated cycling. This makes a typical Li-S battery useless within a few dozen cycles—far too few for a laptop or car battery that may get cycled once a day for years.
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