Dr. Kyeongjae Cho, professor of materials science and engineering in the Erik Jonsson School of Engineering and Computer Science, has discovered new catalyst materials for lithium-air batteries that jumpstart efforts at expanding battery capacity.
“There’s huge promise in lithium-air batteries. However, despite the aggressive research being done by groups all over the world, those promises are not being delivered in real life,” Cho said. “So this is very exciting progress. (UT Dallas graduate student) Yongping Zheng and our collaboration team have demonstrated that this problem can be solved. Hopefully, this discovery will revitalize research in this area and create momentum for further development.”
The lithium-air battery, Li-air for short, is a metal-air battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. The theoretical specific energy of a non-aqueous Li-air battery (in the charged state with Li2O2 product and excluding the oxygen mass) is ~12 kWh per kg. This is comparable with the theoretical specific energy of gasoline (~13 kWh per kg). In practice, the Li-air batteries with a specific energy of ~1.7 kWh per kg at the cell level have been developed, which is about 5 times greater than that of commercial lithium-ion batteries, and which is sufficient to run a Fully Electric Vehicle (FEV) for 500 km (311 miles) on a single charge
Research by Cho and Yongping Zheng (pictured) focuses on the electrolyte catalysts inside the battery, which, when combined with oxygen, create chemical reactions that create battery capacity
Lithium-air (or lithium-oxygen) batteries “breathe” oxygen from the air to power the chemical reactions that release electricity, rather than storing an oxidizer internally like lithium-ion batteries do. Because of this, lithium-air batteries boast an energy density comparable to gasoline — with theoretical energy densities as much as 10 times that of current lithium-ion batteries, giving them tremendous potential for storage of renewable energy, particularly in applications such as mobile devices and electric cars.
For example, at one-fifth the cost and weight of those presently on the market, a lithium-air battery would allow an electric car to drive 400 miles on a single charge and a mobile phone to last a week without recharging.
Practical attempts to increase lithium-air battery capacity so far have not yielded great results, Cho said, despite efforts from major corporations and universities. Until now, these attempts have resulted in low efficiency and poor rate performance, instability and unwanted chemical reactions.
Cho and Zheng have introduced new research that focuses on the electrolyte catalysts inside the battery, which, when combined with oxygen, create chemical reactions that create battery capacity. They said soluble-type catalysts possess significant advantages over conventional solid catalysts, generally exhibiting much higher efficiency. In particular, they found that only certain organic materials can be utilized as a soluble catalyst.
Based on that background, Cho and Zheng have collaborated with researchers at Seoul National University to create a new catalyst for the lithium-air battery called dimethylphenazine, which possesses higher stability and increased voltage efficiency.
“The catalyst should enable the lithium-air battery to become a more practical energy storage solution,” Zheng said.
According to Cho, his catalyst research should open the door to additional advances in technology. But he said it could take five to 10 years before the research translates into new batteries that can be used in consumer devices and electric vehicles.
Cho said he has been providing research updates to car manufacturers and telecommunications companies, and said there has been interest in his studies.
“Automobile and mobile device batteries are facing serious challenges because they need higher capacity,” he said.
“This is a major step,” Cho said. “Hopefully it will revitalize the interest in lithium-air battery research, creating momentum that can make this practical, rather than just an academic research study.”
The discovery of effective catalysts is an important step towards achieving Li–O2 batteries with long cycle life and high round-trip efficiency. Soluble-type catalysts or redox mediators (RMs) possess great advantages over conventional solid catalysts, generally exhibiting much higher efficiency. Here, we select a series of organic RM candidates as a model system to identify the key descriptor in determining the catalytic activities and stabilities in Li–O2 cells. It is revealed that the level of ionization energies, readily available parameters from a database of the molecules, can serve such a role when comparing with the formation energy of Li2O2 and the highest occupied molecular orbital energy of the electrolyte. It is demonstrated that they are critical in reducing the overpotential and improving the stability of Li–O2 cells, respectively. Accordingly, we propose a general principle for designing feasible catalysts and report a RM, dimethylphenazine, with a remarkably low overpotential and high stability.
SOURCES- University of Texas at Dallas, Nature Energy, Wikipedia