Beyond Li-Ion: Researchers Pursuing Lithium and Zinc Air Batteries
By John O'Dell June 1, 2010
By Rick Popely, Contributor
Lithium-ion batteries are boosting the viability of hybrids, plug-ins and electric vehicles because of their greater energy density compared to other batteries, but researchers are already working on the next big thing, which could involve lithium or a metal such as zinc and something that is readily available and free - oxygen.
Lithium-air batteries are receiving serious attention at Argonne National Laboratory and elsewhere because they have potential for delivering five to 10 times the energy density of lithium-ion, today's state-of-the-art.
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Argonne National Lab diagram of lithium-air battery .
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And at least one company, ReVolt Technology, a small Switzerland-based startup, is researching zinc-air batteries, which are a bit less energy dense but a lot cheaper than lithium-air.
ReVolt recently received a $5 million federal Energy Department grant to research zinc-air batteries, which proponents say have three times the energy density of lithium-ion cells and use a chemical element - zinc - that is less expensive than lithium and more widely available.
Though lithium-ion chemistry provides the is best batteries available today for grid-rechargeable electric-drive vehicles, it still poses safety issues because of its volatility. There also are energy security issues because it is available in only a few parts of the world and would replace dependency imported oil with dependency on imported lithium.
And while it is superior for long-distance electric driving than the nickel-metal hydride batteries used in conventional hybrids, it also is more expensive, raising the cost of vehicles that use lithium-ion.
Neither lithium-air nor zinc-air has been proven in the real world, and even if either pans out it in R&D testing, commercialization could be several years away.
Smaller, Stronger
But researcher are excited because both offer the potential for a battery pack that could deliver 20 to 400 miles of travel on a single charge in a smaller and lighter package than lithium-ion chemistry permits - traits that make them appealing for use in vehicles.
"They could be half the size and provide double the range," Khalil Amine, manager of the advanced lithium battery program at Argonne, said of lithium-air batteries.
They work by drawing oxygen out of the air and bonding it with lithium to produce a flow of electrons - much like a hydrogen fuel cell combines oxygen and hydrogen to produce electricity. Both fuel cells and lithium-air batteries need catalyst material to work and one of the challenges facing the Argonne team is to find a reliable and cost-effective catalyst material.
Because the lightweight batteries are so energy dense, the could provide a range of well over 200 miles on a single charge, Amine said, erasing much of the "range anxiety" often associated with driving a battery-EV.
He said , though, that he believes the best application for a lithium-air pack would be in plug-in hybrids, which need to deliver only 40 miles or so of range on battery power to meet the daily driving needs of three-fourths of American motorists.
"You don't have to worry about being stuck on the road when the power runs out," Amine said of plug-ins, which use gas engines to augment the batteries and keep the cars rolling once the battery charge is depleted.
"If you use all-electricity on weekdays, you might go to the gas station only four or five times a year. I would like that."
Boosting Staff
Argonne has doubled the number of researchers it has working on technology, to a team of 20, but Amine said even with the increased focus lithium-air batteries are still at least a decade away from commercial viability.
If that sounds like a long time, he said, consider that it took 20 years to double the capacity of lithium-ion batteries to get them to today's performance levels.
Lithium-air isn't an evolution of lithium-ion but "a hybrid system between a fuel cell and a battery, so you have the problems of both fuel cells and batteries," he said, and that will require considerable time and effort to overcome.
Lithium-ion batteries have two electrodes that shuttle lithium ions back and forth through a liquid electrolyte to charge and discharge the battery. The power of the battery depends on the rate the lithium moves between electrodes.
With lithium-air (more correctly, lithium-oxygen), one of the electrodes is a lithium metal anode and the other a lightweight, porous carbon cathode through which oxygen flows.
The carbon cathode would replace the conventional lithium-ion battery electrode made of graphite or other heavier material. Lithium reacts easily with oxygen on the charging cycle, but breaking the elements apart during discharge is more difficult.
One key challenge is to find a durable catalyst that can separate the oxygen from the lithium over a minimum useful lifetime of 10 years.
"The trick is the catalyst," said Daniel Abraham, a materials scientist who works in Argonne's advanced lithium program. "That is the magic material you need to break the bond and be able to repeat this over thousands of cycles."
Think Zinc
While lithium-air sounds great, James P. McDougall, chief executive of ReVolt Technology, heads a team that is trying to prove that zinc-air batteries can provide nearly as much power at lower cost.
He said he believes zinc-air and lithium-ion batteries can coexist in the market and even work side-by-side in electric-drive vehicles.
Zinc-air batteries are built of layers of flat "plates" of zinc, a catalyst, an electrolyte and a porous membrane...
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Small lithium-ion packs could provide short power bursts for city driving and acceleration from low speeds, while lower-cost, higher-density zinc-air batteries would furnish the power for long-distance cruising, giving EVs the range they now lack at a more affordable price.
"Every battery technology has its strengths and weaknesses. There is no silver bullet out there that does everything well," McDougall said in a telephone interview from Switzerland.
"If we are successful we could be an enabler for lithium-ion for vehicle applications. We really think we can make lithium-ion a compelling complement to zinc-air."
McDougall estimates that the cost of zinc-air batteries could be as little as one-fifth the cost of lithium-ion batteries because zinc is much cheaper and easier to find that lithium. Additionally, zinc-air batteries wouldn't need the expensive thermal safety precautions required for lithium.
Long Road
ReVolt, which plans to open a U.S. headquarters in Portland, Or., later this year, said it will use its government grant to develop a zinc-air demonstrator unit over the next three years.
If the project is successful, ReVolt will continue development with a prototype vehicle battery pack. McDougall projects it will be five to seven years before the company is ready to begin testing batteries in vehicles.
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...that,when packaged, make a compact flat cell.
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Zinc is widely used today in small, button-type hearing-aid batteries and other applications, but none of the present zinc-air batteries is rechargeable.
That means ReVolt is plowing new ground by developing a large, rechargeable battery pack that has to last for years in the rough-and-tumble life of a vehicle.
In zinc-air batteries, the anode is zinc and the air in the battery serves as the cathode. A key issue facing ReVolt is the same as that facing the Argonne researchers - development of a stable catalyst that can endure thousands of charge and discharge cycles.
McDougall says overcoming such challenges could provide a breakthrough in automotive battery technology.
"What is compelling about zinc-air is that it represents three times the energy density of the current state-of-the-art (li-ion) at a fraction of the cost," he said.
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Interesting, could be the game changing technology needed to make electric cars mainstream.
Huge number of other potential applications besides cars too.
http://lifepo4.info
This looks like a very promising technology and will be a catalyst for all different form of electric mobility. Until both Lithium-Oxygen and Zinc-Oxygen are ready for production Lithium Iron Phosphate (LiFePO4) is the way to go.
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