A research group that includes Professor Atsuo Yamada, Associate Professor Masashi Okubo, Doctoral Researcher Xiangmei Shi, graduate student Akihisa Tsuchimoto and others at the Department of Chemical System Engineering, School of Engineering, the University of Tokyo, has discovered an electrode material that is capable of storing electrical energy without losing energy as heat, even when oxygen electrons are used.
The lithium-ion batteries that are currently used are limited in the electrical energy they can store, making it necessary to increase the capacity of the transition metal oxides that serve as the electrode material. Attempts to use the redox reaction of the oxygen contained in transition metal oxides for electricity storage have been being carried out for many years, but when oxygen is oxidized the oxygen atoms combine, and consequently a significant amount of the stored electrical energy is lost as heat energy. As a result, this approach is inefficient as electricity storage, and applying it practically has proven difficult.
The research group discovered that the oxygen electrons that the electrode material Na2Mn3O7 possesses are capable of storing electrical energy without energy loss. This electrode material is charged at 4.23V, 4.55V to eliminate Na+, and simultaneously the oxygen releases electrons to store electrical energy. Next, when electrical discharge takes place Na+ is inserted and the oxygen absorbs electrons to supply electrical energy. If this electrical discharge is carried out at 4.19V, 4.52V, there is only an extremely small difference in electrical potential between the charge and the discharge, of 0.04V, 0.03V, so electrical energy can be stored and supplied with almost no loss.
When the research group magnetically measured the state of the oxygen electrons in order to study the reason why electrical energy loss was not occurring, it found that the electrons of the oxygen atoms were existing stably in a released state (a ligand hole).
Professor Yamada says that “Drawing on this knowledge to develop electrode materials capable of preventing the formation of oxygen atom bonds, which causes energy loss, and in particular, accelerating materials development by extracting the transition metal ions that interact strongly with the oxygen atoms, will contribute to increasing the capacity of batteries.”