Impact of tetracyanoethylene plasticizer on PEO based solid polymer electrolytes for improved ionic conductivity and solid-state lithium-ion battery performance

Poly(ethylene oxide) is a promising material for solid-state lithium batteries due to its safety, ease of processing, and compatibility with lithium. However, conventional linear PEO falls short of practical requirements due to its limited ionic conductivity, a consequence of the high crystallinity of its ethylene oxide chains. This crystallinity hinders the movement of lithium ions, limiting its performance in solid-state battery applications. In this study, we successfully prepared the plasticized solid polymer electrolytes (PSPEs) based on poly(ethylene oxide) (PEO)/ tetracyanoethylene (TCE) complexed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and studied the effect of TCE on structural, mechanical, electrical and electrochemical properties of PSPEs. The addition of tetracyanoethylene effectively disrupts the crystallinity of the PEO matrix, as confirmed by X-ray diffraction analysis. The addition of TCE also enhanced the elongation-at-break of the PEO12-LiTFSI system, indicating improved flexibility. Consequently, the ionic conductivity of the SPEs increases with increasing tetracyanoethylene content, reaching a maximum of 1.14 x 10- 4 S/cm at 25 degrees C for the electrolyte containing 30 wt% of tetracyanoethylene. Furthermore, the plasticized SPEs exhibit a wide electrochemical stability window, as determined by linear sweep voltammetry. Solid-state battery tests demonstrate a high initial discharge capacity of 143.5 mAhg-1 at 0.1C along with good cycling performance.