Aqueous synthesis of lithium superionic-conducting complex hydride solid electrolytes

Abstract

Solid electrolytes are key materials in all-solid-state batteries because their ionic conductivity and stability determine battery performances, such as energy density and power density. However, most existing superionic-conducting solid electrolytes suffer from structural decompositions in moist environment, mainly due to the instability of the solid electrolytes against water, limiting their use in practical cells. Herein, we report the water stability and water-mediated synthesis of complex hydride solid electrolytes. Lithium complex hydrides containing polyanionic closo-type complex anions are dissociated into lithium cations and complex anions in an aqueous solvent without decomposition and are recrystallized to the pristine structure after the removal of water solvent. Taking advantage of this conspicuous water-stability, we propose a simple aqueous liquid-phase synthesis for lithium superionic-conducting complex hydrides. In addition, high-voltage NCM/Li all-solid-state batteries employing the complex hydride prepared by the aqueous synthesis as an anolyte exhibit good battery performance. The current study suggests that an intrinsic water-stable property of closo-type complex hydrides can be leveraged in material and battery processes under a moisture environment.