AUVAC

Assessing The Safety Of Lithium-Ion Batteries

February 11, 2013 via – Chemical and Engineering News

Lithium-ion batteries are back in the crosshairs after two safety incidents aboard Boeing 787 Dreamliner airplanes in January. Headlines everywhere drew readers to stories about flaming and smoldering batteries. Reports warned of these popular power packs’ tendency to overheat and burst into flames. Broadcasts pointed out that fires in portable electronic devices several years ago prompted manufacturers to recall millions of Li-ion laptop batteries.

But these batteries are statistically very reliable. “There’s a lot of mythology in the area of lithium-ion battery safety,” says Brian M. Barnett, a battery safety specialist at Lexington, Mass.-based technology development firm Tiax. Failure rates for rechargeable Li-ion batteries are on the order of one in 10 million cells, he says. “That’s not a reliability problem. It’s an exception.”

Yet exceptions can still be dangerous. As a result of the enormous number of Li-ion cells manufactured each year—about 4 billion in 2012, according to Barnett—some of those failures can lead to fires and serious safety incidents. Although the probability is tiny, the potential for mishap grows as Li-ion battery use surges. Adding to the concern is the scale issue. Li-ion batteries range from palm-sized or smaller packs weighing an ounce or less to 400-plus-lb electric vehicle batteries, and the larger devices can cause more serious problems if they fail.

Exploring the oceans – 20,000 colleagues under the sea

January 9, 2013 via – The Economist

SAILING the seven seas is old hat. The latest trick is to glide them. Sea gliders are small unmanned vessels which are now cruising the briny by the hundred. They use a minuscule amount of power, so they can stay out for months. And, being submarines, they are rarely troubled by the vicissitudes of weather at the surface. Their only known enemies are sharks (several have come back covered in tooth marks) and fishing nets.

Sea gliders are propelled by buoyancy engines. These are devices that pump oil in and out of an external bladder which, because it deflates when it is empty, means that the craft’s density changes as well. This causes the glider to ascend or sink accordingly, but because it has wings some of that vertical force is translated into horizontal movement. Such movement is slow (the top speed of most gliders is about half a knot), but the process is extremely efficient.

That means gliders can be sent on long missions. In 2009, for example, a glider called Scarlet Knight, operated by Rutgers University, in New Jersey, crossed the Atlantic on a single battery charge, though it took seven months to do so.

Since that crossing, gliders have been deployed on many previously unthinkable missions. In 2010 teams from the American navy, the Scripps Institution of Oceanography and iRobot, a robot-maker based in Bedford, Massachusetts, used them to track the underwater effects of the Deepwater Horizon oil spill in the Gulf of Mexico. That same year a glider owned by Oregon State University watched an underwater volcano erupting in the Lau basin near Tonga. In 2011 a glider made by another firm, Teledyne Webb of East Falmouth, also in Massachusetts, tracked seaborne radiation leaked from the tsunami-damaged reactors in Fukushima, Japan. And the University of Newfoundland is planning to use gliders equipped with sonar to inspect icebergs, to work out whether they are a threat to underwater cables and other seabed infrastructure.