Move over, lithium-ion. A start-up company in northwestern Montana reports that it has solved the rechargeable problem that has dogged zinc-air battery development and will soon be in competition with the dominant lithium-ion technology.
Ron Brost, CTO and CEO of ZAF Energy Systems, reports his research team has developed a zinc-air prototype that produces two times the energy of a lithium-ion battery at a third of the cost, with applications ranging from powering cell phones to airplanes.
The technology, which has four (or pending) patents, was developed by an offshoot of four-year-old ViZn Energy Systems (formerly Zinc Air, Incorporated), which is beginning to commercialize its zinc-iron redox grid batteries.
Advantages of zinc over lithium-ion are many and obvious: zinc is a readily available and cheap mineral, with resources totaling 1.9 billion tons worldwide; it costs about a third what lithium costs; it weighs about half what lithium weighs in comparable applications; and while lithium-ion batteries have caught fire under certain trials, zinc is environmentally benign, going to zinc oxide (the main component of baby powder) after playing out in a battery. And zinc oxide is easily recyclable; Brost claims the ZAF battery itself will be recyclable.
But let’s look at what ZAF scientists say their prototype can do. Brost wrote in a white paper that research institutes and industrial labs have verified the basic function of rechargeable zinc-air cells, but three basic problems have remained: the air catalyst must be stable and convert oxygen to hydroxide during discharge and evolve oxygen during charges; the zinc electrode must be protected against air oxidation in order to prevent self-discharge and must be able to be formed and reformed hundreds of times without loss of energy or shorting the cell; and the alkaline electrolyte cannot lose water as it is exposed to a continual stream of air, nor can it react with air contaminants such as carbon dioxide.
Brost says the ZAF prototype battery solves these problems.
First, they’ve achieved 400 Wh/kg when, previously, 180 Wh/kg was the norm with zinc-air batteries, which means that the prototype has achieved at least two times the energy output of currently used lithium-ion batteries. They’ve developed a highly efficient bi-directional air cathode and made all three components of the battery bi-directional. And they have developed the first solid-state electrolyte to be used in a battery. Instead of a typical liquid or paste alkaline electrolyte, the ZAF battery uses a solid polymer electrolyte that limits the amount of oxygen that can pass through, while allowing ions to pass freely. This substantially increases the number of recharges and extends the battery life.
Brost notes that problems of dendrites forming in zinc batteries are addressed through proprietary anode and electrolyte designs that both limit dendrite growth and prevent shorting.
Howard Wilkins, chairman emeritus at ViZn and holder of a patent on the ZAF battery, reports that ZAF licensed a fuel cell technology developed at Lawrence-Livermore National Labs. “The technology was a fuel cell that was mechanically rechargeable [it had to be rebuilt to recharge]. We found a way to make it electronically rechargeable. That increased the energy by 300 percent and then we made it rechargeable,” he says.
He says the electrolyte in the ZAF battery has been proven rechargeable at 500 charges and researchers are “trying to get beyond that.” When asked if 500 charges would be sufficient, Wilkins noted that a ZAF battery lasts almost three times as long as today’s batteries, so in a cell phone, for example, a ZAF battery might only need to be charged once a week rather than several times a week.
One of the main applications ZAF is aiming its research toward is the electric car battery. Brost has about 12 years of experience in leading battery teams at Ford Motors and Coda Automotive. He said one of ZAF’s challenges is to “get the cycle life up,” but added that the ZAF battery stores a lot more energy than other batteries. “If we build an electric vehicle with a 500-mile battery, with 500 recharges, that’s 250,000 road miles, so we’re looking at it that way. Five hundred cycles is a reasonable customer expectation,” he says.
Wilkins, a former medical researcher and one of the pioneers of the soft contact lens, says the ZAF technology is in some ways similar to contact lens chemistry. In doing research at Pennsylvania State University and Oak Ridge National Labs, Wilkins says researchers were looking for a material for the contact lens that let oxygen in. Conversely, with the zinc fuel battery, they were looking for a way to make the electrolyte ionically conductive, but oxygen limiting.
Another member of Brost’s team was discovered as a postdoc at Montana State University. Adam Weisenstein had been researching compounds for catalysts for years at MSU. Weisenstein became a member of the ZAF team and developed a special formula for the perovskite used in the battery catalyst, which was essential for the creation of an efficient bi-directional cathode. Today Weisenstein is a senior scientist at ZAF.
That is part of the “serendipity” Brost refers to in the ZAF research that has led to today’s prototype. He says he’s been surprised at how fast their research has developed – a matter or a year or two as opposed to typically three to five years. “It evolved as a very simple but very elegant system,” he says. “The individual components are interesting enough, but putting them together in this trinity of technologies will give us a very superior commercial product.”
Thomas Zawodzinski, Governor’s Chair in Electrical Energy Storage at the University of Tennessee Knoxville, has verified the general claims made by Brost and Wilkins. “They’ve got something that works. They definitely have a rechargeable battery,” he said in an interview, adding, “It’s always a question of efficiency.”
Zawodzinski, who holds a chair at Oak Ridge National Labs, says he considers ZAF in the early prototyping stage — “a process of continual improvement of these materials.” He says he tested the ZAF battery in his lab and “we more or less validated the performance they’re showing.”
Zawodzinski is leading a team of researchers from Penn State, Case-Western University, and the University of Memphis to synthesize new materials for use in the ZAF electrolyte.
Brost reports that they are testing for conductivity and water chemistry and trying various materials developed by Zawodzinski’s team in their batteries. “We’re looking for a long-life battery that is robust at different temperatures, humidities, and latitudes,” he says.
ZAF’s commercialization model is to license its technology, and they are in talks with several companies. Brost predicted commercialization for small applications, such as hearing aides, will take about a year and EV batteries three to five years.
ZAF and ViZn Energy, located in Columbia Falls, Montana, have kept a low profile and operate through funds provided by investors. Together they employ about 70 people.
About the Author: Joan Melcher is a freelance writer and editor who focuses on energy and the environment. Her stories have appeared in Pacific Standard, BioCycle, High Country News, and chinadialogue.com.