Thermally Stable Ceramic-Salt Electrolytes for Li Metal Batteries Produced from Cold Sintering Using DMF/Water Mixture Solvents

Abstract

The cold sintering process (CSP) for synthesizing oxide-based electrolytes, which uses water transient solvents and uniaxial pressure, is a promising alternative to the conventional high temperature sintering process due to its low temperature (<200 <degrees>C) and short processing time (<2 h). However, the formation of amorphous secondary phases in the intergranular regions, which results in poor ionic conductivity (s), remains a challenge. In this study, we introduced high boiling solvents of dimethylformamide (DMF, b.p.: 153 <degrees>C) and dimethyl sulfoxide (DMSO, b.p.: 189 degrees C) as transient solvents to develop composite electrolytes of Li1.5Al0.5Ge1.5(PO4)(3) (LAGP) with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). Our results show that composite electrolytes processed with the DMF/water mixture (CSP LAGP-LiTFSI DMF/H2O) yield a high s of 10(-4) S cm(-1) at room temperature and high relative densities of >87%. Furthermore, the composite electrolytes exhibit good thermal stability; the s maintains its initial value after heat treatment. In contrast, the composite electrolytes processed with the DMSO/water mixture and water alone show thermal degradation. The CSP LAGP-LiTFSI DMF/H2O composite electrolytes exhibit long-term stability, showing no signs of short circuiting after 350 h at 0.1 mAh cm(-2) in Li symmetric cells. Our work highlights the importance of selecting appropriate transient solvents for producing efficient and stable composite electrolytes using CSP.