A new class of solid polymer electrolytes (SPEs) is successfully developed by employing poly(ethylene oxide) (PEO) as a polymer host, N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (P12FSI) as an ionic plastic crystal, and lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt. Their properties, including thermal behavior and electrochemical and mechanical characteristics are evaluated. For the as-obtained SPE system, P12FSI combines with PEO-LiFSI uniformly and no phase separation occurs. Such SPEs exhibit high thermal stability, good electrochemical stability, satisfactory ionic conductivity, acceptable mechanical strength and flexibility, as well as the potential to inhibit the lithium dendrite growth. Furthermore, Li/LiFePO4 cells containing the as-prepared SPE at 0.2C rate could exhibit a discharge capacity of about 157 mAh g(-1) at 50 degrees C, with high cycling stability and favorable rate capability. Such SPEs are expected to have great potential for all-solid-state lithium batteries.