Stanford Report, June 4, 2013
Stanford scientists develop efficient zinc-air battery
Stanford scientists have created a zinc-air battery that could become a low-cost alternative to lithium-ion technology.
BY MARK SHWARTZ


Stanford University scientists have created an advanced zinc-air battery with higher catalytic activity and durability than similar batteries made with platinum and other costly catalysts. The results, published in the journal Nature Communications, could lead to the development of a low-cost alternative to conventional lithium-ion technology widely used today, the researchers said.

"There have been increasing demands for high-performance, inexpensive and safe batteries for portable electronics, electric vehicles and other energy storage applications," said Hongjie Dai, a professor of chemistry at Stanford and the lead author of the study. "Metal-air batteries offer a possible low-cost solution."

According to Dai, lithium-ion batteries have attracted the most attention, despite their limited energy density (energy stored per unit volume), high cost and safety problems. "With ample supply of oxygen from the atmosphere, metal-air batteries have drastically higher theoretical energy density than either traditional aqueous batteries or lithium-ion batteries," he said. "Among them, zinc-air is technically and economically the most viable option."

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High-performance electrodes are necessary to catalyze the oxygen-reducing reaction during discharge and oxygen production during recharge, he said. In zinc-air batteries, both reactions are sluggish. In recent years, Dai’s group has used nanotechnology to develop novel electrocatalysts with higher catalytic activity and greater durability than conventional electrodes made with platinum, iridium and other precious metals.

For the Nature Communications study, the research team created electrode catalysts made of cobalt oxide, a nickel-iron compound and carbon nanomaterials. “We found that these catalysts greatly boosted battery performance," Dai said. “We achieved record high-energy efficiency for a zinc-air battery, with a high specific energy density more than twice that of lithium-ion technology."

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How zinc-air batteries work.

By MIT Technology Review on September 1, 2001


In a world gone portable, batteries are key. without those unassuming little power supplies to run our laptops, cell phones and personal digital assistants, we might as well return to the days of paper and pigeons. For as much as batteries offer, though, they still annoy us with their frequent need for recharging or replacement altogether. Lately, the zinc-air battery has been turning up as a new choice of power for handheld electronics, providing up to three times the energy of common alkaline batteries in a more compact package.

Zinc-air cells work like conventional batteries in that they generate electrical power from chemical reactions. But instead of packing the necessary ingredients inside the cell, zinc-air batteries get one of their main reactants-oxygen-from the outside air. Oxygen molecules enter the cell through tiny holes in the top and then come into contact with a positively charged electrode (cathode) made of porous carbon. Water and other molecules already present in the pores of the electrode react with the oxygen to produce hydroxyl. These molecules, and other preexisting hydroxyls, migrate through an air separator to a negatively charged electrode (anode) that consists of a zinc gel. The hydroxyls bond to a zinc molecule to form zincate, which immediately splits into two hydroxyls, a water molecule and zinc oxide, and releases two electrons that travel through a circuit to power a device-usually a cell phone or hearing aid.

Using a reactant from the air saves on space, reducing the size and weight of the battery. And unlike some batteries used in wireless devices, zinc-air cells contain no toxic compounds and are neither highly reactive nor flammable. In fact, they can be recycled, safely disposed of, or in some cases, recharged with new zinc. Their only downside is that constant contact with ambient air can either dry up the zinc gel or, if conditions are too humid, flood it with water vapor. Both render the battery less potent. AER Energy Resources of Smyrna, GA, has found a way to diffuse the air (bottom inset). And another company, Electric Fuel, is developing zinc-air battery technology for automobiles. Instead of sucking gas, our cars could one day be breathing air.