Na5YSi4O12: A sodium superionic conductor for ultrastable quasi-solid-state sodium-ion batteries

Sodium-based solid-state batteries (SSBs) demonstrate great superiority in the state-of-the-art energy storage devices, whereas, their development is impeded because of the limited categories of solid electrolyte (SE) with workable ionic conductivity and good electrochemical stability. Herein, we propose a new kind of hexagonal Na5YSi4O12 with a high room-temperature ionic conductivity of 1.59 × 10−3 S cm−1 and low activation energy of 0.20 eV, benefiting from the inherent three-dimensional Na+ transport pathway and optimized synthesis conditions in favor of achieving a densificated SE pellet. Na5YSi4O12 enables an excellent electrochemical stability to 8.0 V, a stable sodium tripping/plating behavior to 2.2 mA cm−2 and a long-lived cycle over 1200 h. The Na3V2(PO4)3||Na5YSi4O12||Na SSBs deliver comparable performances as those in organic liquid electrolyte, which suggests Na5YSi4O12 is a promising SE candidate. The proposed new structured Na5YSi4O12 as well as the preferred preparation condition could boost the ongoing research for the advanced sodium-based SSBs.