Kousuke Noi

Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries

Innovative rechargeable batteries that can effectively store renewable energy, such as solar and wind power, urgently need to be developed to reduce greenhouse gas emissions. All-solid-state batteries with inorganic solid electrolytes and electrodes are promising power sources for a wide range of applications because of their safety, long-cycle lives and versatile geometries. Rechargeable sodium batteries are more suitable than lithium-ion batteries, because they use abundant and ubiquitous sodium sources. Solid electrolytes are critical for realizing all-solid-state sodium batteries. Here we show that stabilization of a high-temperature phase by crystallization from the glassy state dramatically enhances the Na(+) ion conductivity. An ambient temperature conductivity of over 10(-4) S cm(-1) was obtained in a glass-ceramic electrolyte, in which a cubic Na(3)PS(4) crystal with superionic conductivity was first realized. All-solid-state sodium batteries, with a powder-compressed Na(3)PS(4) electrolyte, functioned as a rechargeable battery at room temperature.

Preparation and characterization of highly sodium ion conducting Na3PS4–Na4SiS4 solid electrolytes

This study investigated electrical and electrochemical properties of (100 − x)Na3PS4·xNa4SiS4 (mol%) glass–ceramics prepared using mechanical milling and consecutive heat treatment. Glass–ceramics at the compositions of 0 ≤ x ≤ 10 exhibited higher conductivity than 10−4 S cm−1 at room temperature, which was achieved by precipitation of cubic Na3PS4 crystal with high sodium ion conductivity. The conductivity increased concomitantly with increasing Na4SiS4 contents at compositions of 0 ≤ x ≤ 6. The glass–ceramic with 6 mol% Na4SiS4 exhibited conductivity of 7.4 × 10−4 S cm−1 at room temperature, which is the highest value reported for Na+ ion conducting sulfides to date. The conductivities of the glass–ceramics in the composition range of 25 ≤ x ≤ 100, where unknown phases are crystallized, were 10−7–10−5 S cm−1. These were lower than the conductivities of the corresponding glasses before heat treatment. The 90Na3PS4·10Na4SiS4 electrolyte showed a wide electrochemical window of 5 V.