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Lithium-iodine battery packs more energy punch

Hye Ryung Byon, Yu Zhao and Lina Wang from the RIKEN Byon Initiative Research Unit developed a lithium-iodine battery system with twice the energy density of conventional lithium-ion (Li-ion) batteries. Despite performing well in consumer electronics, engineers still have difficulty in squeezing enough Li-ion batteries inside vehicles to generate optimal power and range without introducing storage and weight issues. Byon’s team sought to tackle such challenges through alternative energy sources.

In their research they turned to an ‘aqueous’ system in which the organic electrolyte in conventional Li-ion cells is replaced with water. Such aqueous lithium battery technologies have gained attention among alternative energy researchers because of their greatly reduced fire risk and environmental hazard. Aqueous solutions also have other advantages, which include an inherently high ionic conductivity.

For their battery system, the researchers investigated an ‘aqueous cathode’ configuration (Fig. 1), which accelerates reduction and oxidation reactions to improve battery performance. Finding suitable reagents for the aqueous cathode, however, proved to be a tricky proposition. According to Byon, water solubility is the most important criterion for screening new materials, since this parameter determines the battery’s energy density. Furthermore, the redox reaction has to take place in a restricted voltage range in order to avoid water electrolysis. An extensive search led the researchers to produce the first-ever lithium battery involving aqueous iodine—an element with high water solubility and a pair of ions, known as the triiodide/iodide redox couple, that readily undergo aqueous electrochemical reactions.


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