Highly Conductive PEO-Based Polymer Electrolyte for Na Battery Applications

Abstract

State-of-the-art Li- or Na-ion batteries typically use organic solvents in the electrolytes, which might cause serious safety issues. Replacing the liquid electrolytes with nonflammable, dense solid-state electrolytes can potentially solve this problem. Among all types of solid electrolytes, PEO-based polymer electrolytes (PBPEs) have attracted extensive attentions owing to their excellent flexibility, chemical stability, and easiness for processing. However, their relatively low ionic conductivities limit the applications in batteries. Here, we reported our recent progress to develop a class of highly conductive PBPEs for Na battery applications. Through addition of a moderate amount of ionic liquid (e.g., EMITFSI) to PEO, a significant amount of amorphous phase was detected in the polymer, which is critical to achieve high ionic conduction. Addition of 5~15 wt.% NaTFSI to the composite further increased the content of the amorphous phase and eventually led to a nearly 100% amorphous. The total ionic conductivities of the PBPE with 15 wt.% NaTFSI were as high as 0.59 and 2.07 x 10-3 S/cm at RT and 50oC, respectively, which is significantly higher than those of traditional PBPEs. In this study, the electrochemical, chemical, and mechanical properties and performance of the PBPEs have been thoroughly investigated, which indicated this type of PBPEs is very promising as a membrane for all-solid-state Na battery applications.