PolyPlus is currently testing lithium metal-seawater batteries in conjunction with the Monterey Bay Aquarium Research Institute to determine whether they can withstand real working conditions. One concern is that microorganisms in the ocean will grow on the batteries' surface and impair their operation, although preliminary tests have produced good results.

The single-use batteries made by the company employ a piece of lithium metal about two centimeters squared and three millimeters thick; they have a storage capacity close to that of the lithium-ion batteries in today's laptops at one-fifth the weight. The company has partnered with battery manufacturer Quallion to produce batteries based on PolyPlus's electrode designs and will make batteries under contract for an undisclosed government agency. Quallion says that lithium-metal electrodes can be processed using much of the infrastructure already in place for making lithium-ion batteries. "Certain precautions are needed to handle the material, but there are no tricks to it," says Beach.

Lithium-metal batteries have the potential to be "transformational" for underwater applications, says James Bellingham, the Monterey Bay Aquarium Research Institute's chief technologist. Most ocean research takes place close to shore because, as Bellingham says, "in the ocean, there are no plugs" for recharging the sensor-laden autonomous craft that monitor the seas. Higher energy-density batteries could enable much better monitoring of the effects of climate change on the planet, says Bellingham.