Katsuya Teshima

Abstract:

Lithium ion secondary batteries (LIBs) have been extensively studied because of their potential use as power sources in mobile electronics, hybrid-electric vehicles and next-generation electric mobilities. Recently, we are especially focusing on all-crystal (solid)-state LIBs. They have attracted significant attention due to their high energy densities, that is, originating from the device miniaturization, and high safety caused by their non-flammability. However, there is extremely large innovation gap between general LIBs and all-solid-state LIBs because of difficulties in smooth lithium ion transfer, i.e., diffusion of lithium ions and electrons are interfered at interfaces of different solid materials. Therefore, we have tried to control and design their interfaces between active materials and solid electrolytes and fabricate materials for all-solid-state LIBs on the basis of crystal science and engineering. Water-splitting by photocatalysts have been investigated because of expectation to supply clean and recyclable hydrogen energy. In general, photocatalysts, as represented by TiO2, are activated by only ultraviolet light illumination due to their wide band gap. Although these UV-light-driven photocatalysts can split water in a proper condition, the solar energy conversion efficiency is rather low because UV light energy is just several percent in total energy of sun light on the earth, and visible light accounts for almost half of the solar energy. From the viewpoint of increase the efficiency and industrial application of solar hydrogen production, visible-light-driven photocatalysts have intensively attracted research interests. In particular, oxynitride and nitride semiconductor photocatalysts are one of promising materials for construction of photocatalytic water splitting system. Our group has researched a classic flux method for preparing active materials and solid electrolytes for all-solid-state LIBs, and visible-light-driven photocatalysts for solar hydrogen production, and developed flux coating method for fabricating highly crystalline layers on metal collectors. The flux method is a nature-mimetic liquid phase crystal growth technique, and has several advantages over other methods like solid state reaction. It is a relatively low-temperature process that requires very simple equipment, and high-quality crystals with well-developed facets can be grown. The details of materials preparation and interfaces design by use of our flux crystal growth concepts will be presented in the SIPS2017 conference.