Kalispell, Mont.-based Zinc Air, Inc. (ZAI) has obtained exclusive rights from LLNL for the mechanically rechargeable zinc air fuel cell (US Patent 5,434,020) invented by John Cooper, a retired LLNL chemist, who is on the ZAI technical Board of Advisors.
The Zinc Air Fuel Cell (ZAFC) consumes zinc metal and atmospheric oxygen to produce electricity, and produces a reaction product consisting of a liquid suspension of zinc oxides and potassium zincate in an alkaline electrolyte. Refueling is achieved by replacing the spent electrolyte and adding more zinc pellets. The Zinc/Air Fuel Cell allows for rapid refueling, as opposed to overnight recharging, which makes multiple shifts a reality. With 10 minute refueling, this technology allows battery use up to 24 hours a day, notes ZAI.
|Self-feeding cells. Source: ZAI. Click to enlarge.|
The cells are self-feeding. Zinc pellets fall into a narrow opening at the top of each wedge-shaped cell. (Diagram right). Because the cell gap is only a little larger than the particles, the particles do not close pack, even when subjected to strong vibrations. Rather, noted Cooper, particle briding and voids develop, resulting in a low packing density of about 40%. Electrolyte flows upward through the cell and hopper to remove heat and reaction products.
The spent electrolyte can be reprocessed to recover electrolyte and zinc fines, which in turn are pressed into pellets. In a 1995 paper, Cooper noted that the cost of the recovery unit is small compared with the cost of the battery because it operates continuously and hence at a lower power level than the battery. In addition, it lacks the expensive air electrode of the zinc/air battery, adding to the lower cost of the ZAFC solution.
Lower cost is one of the key aspects of the renewed interest by some in zinc air fuel cell technology—which had been explored in the 80s and 90s—propelled by the anticipated demand for efficient, low-cost alternatives to lithium for electric vehicle battery production.
ZAI is the second company to license the LLNL ZAFC technology. Power Air Corporation had earlier secured a license; that license agreement terminated in November 2009. Power Air says it is moving ahead with its own ZAFC design.
In truth, new technology often matures in fits and starts over decades. A previous licensee brought marketing and manufacturing expertise to our inventions. Some of that developmental understanding will seep into new incarnations of the zinc air fuel cell.—Annemarie Meike, LLNL business development executive
Lithium primarily is found outside the United States. Worldwide resources of zinc total more than 1.8 gigatons—with more than 35% of that in the United States alone.
Global zinc production in 21 months would be sufficient to produce one billion 10 kWh zinc air batteries—by contrast it would take 180 years of lithium production to produce those same batteries. These figures were quoted in a recent white paper by Meridian International Research, which stated, “Lithium supply and future production will be far from adequate to sustain global electric vehicle production.”
At the moment, most in the auto industry are currently looking to lithium batteries as the power solution for electric vehicles, but those batteries are manufactured primarily outside of the United States and are not cost effective for widespread use. There is enough readily available zinc just in the United States to produce billions of these batteries.—ZAI Co-Founder and President Dave Wilkins
ZAI is in discussions with multiple fleet vehicle manufacturers to develop products for their immediate needs. The company intends to begin development and testing in late 2010 with full-scale field testing in the second quarter of 2011.
Korea-based Leo Motors is also commercializing a ZAFC technology for use as a range extender in its vehicles. (Earlier post.)
US Patent 5,434,020: Continuous-feed electrochemical cell with nonpacking particulate electrode