Herein is reported the performance of ternary polymer electrolytes incorporating ionic liquids, showing higher ionic conductivity over a wide temperature range than binary polymer-salt systems, while guaranteeing higher safety compared to liquid, organic electrolytes or gel electrolytes. In particular, the electrochemical performance and the interactions between poly(ethylene oxide) (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and several pyrrolidinium-based ionic liquids is comparatively investigated. Eight different polymer electrolytes were produced to test the ionic conductivity and long-time (more than 1400 hours) cycling stability in symmetrical lithium cells. Thermal analysis was used to investigate the thermal stability and degree of crystallinity. Six of the eight investigated samples are found fully amorphous at room temperature. In general, the properties of the polymer electrolytes are influenced by both Ionic liquid ions. The ether function in the side chain of the pyrrolidinium increases the ionic conductivity but, in some cases, lowers the thermal and electrochemical stability.