Lithium ion secondary batteries (LIBs) have been widely used as energy-storage system for variety of power devices. It is necessary to further develop LIBs toward high-functional devices, such as electric vehicles and mobile electronics. Nowadays, all solid-state LIBs have been much interested because of a variety of potential advantage, including energy densities, cost, size, safety, and operating temperature. However, there are serious problems to be solved toward practical uses. For example, diffusion of lithium ions at interface between different solid materials, including active materials and electrolytes, is still poor to operate charge/discharge in batteries. Our group has studied high-quality crystals for applications as energy and environmental materials by using a flux method. Flux method is a nature-mimetic liquid-phase crystal growth technique. Fluxes accord to salts, which work as solvent at temperature over their melting and / or eutectic points. By using fluxes, it is possible to construct specific crystal-growth field at any temperature with facile setup, and give designed crystals regarding to shape, including crystal faces, which has never achieved using other methods like solid state reaction.

Recently, we have applied the flux method to battery materials to create “all-crystal (solid)-state LIBs”. We have expected that flux crystal growth gave (I) crystal-shape control of active materials, (II) construction of good interfaces in electrodes among cathodes, solid electrolytes, and anodes. The second topics would be possible if electrode materials can be dissolved and densely recrystallized on their surfaces. As a result, smooth ionic transportation through bulks and their interfaces would be realized in all-crystal (solid)-state LIBs. Our concept using flux method would provide new aspect to lead an innovation in all solid state LIBs as next-generation energy storage. In the presentation, the details of interfacial and crystal designs of a variety of battery materials will be introduced, coupled with their crystallographic, ionic, and battery properties.

Acknowledgement

This work was supported by JST CREST Grant Number JPMJCR1322 in Japan and Program for Building Regional Innovation Ecosystems of MEXT.