Inhibition of Crystallization of Poly(ethylene oxide) by Ionic Liquid: Insight into Plasticizing Mechanism and Application for Solid-State Sodium Ion Batteries.

All-solid-state sodium ion batteries (ASIBs) possess enhanced safety and desired cycling life compared with conventional liquid sodium batteries, showing great potential in large-scale energy storage systems. Polymer electrolytes based on poly(ethylene oxide) (PEO) have been extensively studied for ASIBs due to superior flexibility and processability. However, PEO-based electrolyte without any modification can hardly meet the requirements of ASIBs at room temperature. In the past decade, unremitting efforts have been attached to inhibiting crystallization of PEO, especially via ionic liquid plasticizing. However, the plasticizing mechanism is not clear. Here we incorporated PyrFSI into PEO-NaClO electrolyte to investigate the plasticizing effect by infrared spectrum characterizations and DFT calculations. The results indicate that FSI anions tend to adhere to the PEO backbone, generating enhanced coordination ability and more coordination sites. Solid-state sodium ion batteries using PEO-NaClO-40 wt % PyrFSI as polymer electrolyte exhibit good cycling and rate performance. Insights into the plasticizing mechanism contribute to fabricating polymer electrolyte with high performance for ASIBs.