When lithium-ion batteries were first introduced as replacements for older, heavier nickel-metal hydride (NiMH) batteries, they offered a breakthrough in greater energy density and lighter weight. This technology has made its way through the field of consumer electronics, and lithium-ion batteries are now ubiquitous. The next step in battery technology may come from the University of Waterloo, where Dr. Linda Nazar is working to develop lithium-sulfur batteries with promising characteristics including three to five times the storage of current lithium-ion batteries.
While most current electric vehicles and hybrids, including the Toyota Prius and the Honda Insight, use NiMH batteries, lithium-ion is beginning in their next generation as well. The Tesla Roadster uses lithium-ion batteries as will the Chevy Volt. A lithium-sulfur battery of comparable weight for a vehicle could significantly extend its range, allowing for more flexible use in an all-electric mode. Or, with the increased energy density available, a vehicle with a similar range could be made significantly lighter through the use of a much smaller lithium-sulfur battery.
Sulfur is currently a component in other large scale storage systems, such as sodium-sulfur batteries, but those require high temperatures and are better suited to fixed location applications, such as grid storage, rather than for portable use. Lithium-sulfur batteries may make sulfur storage energy available in a more portable form.
The lithium sulfur batteries are created by creating assemblies of carbon nanorods that are coated with molten sulfur to fill the voids. The nanoscale structure sets up conditions to keep the sulfur in contact with the carbon, allowing for the repeated charging and discharging necessary for useful rechargeability.
Lithium sulfur batteries have the potential to significantly reduce the size of batteries because they have a higher energy density than other comparable lithium-based batteries.
“This composite material can supply up to nearly 80 percent of the theoretical capacity of sulphur, which is three times the energy density of lithium transition metal oxide cathodes, at reasonable rates with good cycling stability,” said Dr. Nazar.
Sulfur's availability and low cost may help bring this technology to market. The research team has filed for patents on their process and are working on developing it commercially. According to a press release announcing the research publication, sulfur is a less-expensive material than many others used in lithium-based batteries. "It has always showed great promise as the ideal partner for a safe, low cost, long lasting rechargeable battery, exactly the kind of battery needed for energy storage and transportation in a low carbon emission energy economy."
written by Mark, June 09, 2009
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