All-Crystal-State Lithium-Ion Batteries: Innovation Inspired by Novel Flux Coating Method.

All-solid-state lithium-ion rechargeable batteries (LIBs) consisting of solid electrolyte materials have attracted a number of research interests because no use of organic liquid electrolyte increases packaging density and intrinsic safety of LIB, which contribute the development on environmentally-friendly automobiles such as electric vehicle (EV), hybrid vehicle (HV), and plug-in hybrid vehicle (HEV), in addition to efficient utilization of electric energy in smart grid. Among various solid electrolytes, inorganic electrolyte materials have achieved relatively high lithium-ion conductivity and better stability at an ambient atmosphere. Nevertheless, there is a drawback that is relatively high internal resistance owing to relatively slow Li ion movement caused by low crystallinity of materials, scattering at interfaces such as current collector/electrode active materials and electrode active materials/electrolyte materials. In this context, we have proposed a concept, all-crystal-state LIB, in which all the component materials have high crystallinity and those interfaces are effective for Li ion diffusion. Here, we present the fabrication of oxide crystals and crystal layers via flux method and flux coating. Flux method is one of the solution processes in which idiomorphic highly crystalline materials can be obtained under the melting point of the target ones. In addition, it provides simple, low-cost and environmentally-benign pathway compared to conventional solid-state-reaction method. Flux coating method is developed to fabricate high-quality crystal layers (films) on various substrates. High-quality crystals and crystal layers of cathode, anode and electrolyte materials were successfully fabricated.