The development of solid electrolyt

The development of solid electrolytes with the combination of high ionic conductivity, electrochemical stability, and resistance to Li dendrites continues to be a challenge. A promising approach is to create inorganic–organic composites, where multiple components provide the needed properties, but the high sintering temperature of materials such as ceramics precludes close integration or co-sintering. Here, new ceramic–salt composite electrolytes that are cold sintered at 130 °C are demonstrated. As a model system, composites of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) or Li1+x+yAlxTi2−xSiyP3−yO12 (LATP) with bis(trifluoromethanesulfonyl)imide (LiTFSI) salts are cold sintered. The resulting LAGP LiTFSI and LATP–LiTFSI composites exhibit high relative densities of about 90% and ionic conductivities in excess of 10−4S cm−1 at 20 °C, which are comparable with the values obtained from LAGP and LATP sintered above 800 °C. It is also demonstrated that cold sintered LAGP–LiTFSI is electrochemically stable in Li symmetric cells over 1800 h at 0.2 mAh cm−2. Cold sintering provides a new approach for bridging the gap in processing temperatures of different materials, thereby enabling high-performance composites for electrochemical systems.