Lithium-ion conducting oxide single crystal as solid electrolyte for advanced lithium battery application.

Today, all-solid-state secondary lithium-ion batteries have attracted attention in research and development all over the world as a next-generation energy storage device. A key material for the all-solid-state lithium batteries is inorganic solid electrolyte, including oxide and sulfide materials. Among the oxide electrolytes, garnet-type oxide exhibits the highest lithium-ion conductivity and a wide electrochemical potential window. However, they have major problems for practical realization. One of the major problems is an internal short-circuit in charging and discharging. In the polycrystalline garnet-type oxide electrolyte, dendrites of lithium metal easily grow through the void or impurity in grain boundaries of the sintered body, which causes serious internal short-circuits in the battery system. To solve these problems, we present an all-solid-state battery system using a single-crystal oxide electrolyte. We are the first to successfully grow centimeter-sized single crystals of garnet-type by the floating zone method. The single-crystal solid electrolyte exhibits an extremely high lithium-ion conductivity of 10 S cm at 298 K. The garnet-type single-crystal electrolyte has an advantageous bulk nature to realize the bulk conductivity without grain boundaries such as in a sintered polycrystalline body, and will be a game-changing technology for achieving highly safe advanced battery systems.