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Development of Life ExtensionTechnology for Next Generation Lithium Air Batteries

Next generation large capacity batteries: A key to the popularity of EVs

Historically, automobiles were a measure and an aggregate of an era’s technology. Today, electric vehicles, or EVs, are also a collection of state-of-the-art technologies and an icon of eco-friendly technology. EVs have various advantages over conventional internal combustion engine cars such as no exhaust gas and a remarkably low level of noise. Several companies around the world have been involved in the development of EVs, and some of them have also launched commercial products. The core of EV technology is the battery, which serves as the vehicle’s power source. Currently, most of the EVs employ lithium-ion batteries, but their capacities are reaching their limits, making it impossible for the EVs’ driving distance to match that of existing vehicles, even when the lithium battery of maximum capacity to date is used. The introduction of next-generation high-capacity batteries, therefore, have become an indispensable element in popularization and distribution of the EVs.

Lithium air batteries: The next big thing in the next generation battery market

Currently, various next-generation high-capacity batteries that exceed the limitations of existing ones are being developed, and the most notable among those are lithium air batteries. Also known as next-generation dream cells, lithium air batteries are secondary batteries that generate and store electricity through the electrochemical reaction of lithium and oxygen in the air. Lithium air batteries are expected to be the ultimate secondary battery that enable the EVs to overcome their short driving distance. This is because, theoretically, lithium air batteries can achieve an energy density 5 to 10 times higher than that of conventional secondary batteries with a 5 to 6 times lower energy generation cost. However, lithium air batteries have two significant disadvantages such as a low energy efficiency and rapid lifetime degradation due to lithium having a low reversibility at the positive electrode and a high reactivity at the negative electrode. Among the two limitations, the low reversibility in the positive electrode has been remarkably improved as a new method was suggested where a liquid catalyst called the “redox mediator” is introduced into the electrolyte. However, the rapid decrease in the lifespan due to the loss of mediators from the reaction between the mediators and lithium metal electrode still remains unresolved.

Significant increase in the lifetime of lithium air batteries

Against this backdrop, a technology that can solve the short lifetime of lithium air batteries has been developed by domestic researchers. Prof. Hee Tak Kim and Prof. Jung Ki Park and their joint team from the Department of Chemical and Biomolecular Engineering at KAIST (President: Sung-Mo Kang) said they have developed a technology that can extend the lifetime of lithium air batteries by three times. The team introduced an organic-inorganic hybrid protective layer consisting of a gel polymer capable of conducting lithium ions and alumina inorganic particles on the surface of the lithium metal negative electrode. The protective layer interferes with the reaction between lithium and the redox mediator, thereby suppressing the loss of the mediator and the growth of the surface lithium dendrite. As a result, they succeeded in extending the lifecycle by about three times through continuing the effect of the mediators. In addition, the protective layer lowers the high reactivity of the cathode as well as the lithium anode, resulting in a synergistic effect that also improves stability. The result of this research, which was supported by the National Research Foundation of Korea’s General researcher Project and the Climate Change Response Technology Development Project, was published in an online issue (Feb 3, 2016) of Advanced Materials, a prominent international academic journal in the field of materials science. The research was also selected as a Front Inside Cover in recognition of its excellence. Prof. Kim said, “This study provides us clues to overcome the lifetime limitations of lithium air batteries, which are in the spotlight as a next-generation energy storage device.” He continued, “This could be a useful strategy for the practical application of lithium air batteries.”

Prof. Kim, Hee Tak
2016 Annual Report

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