Gel polymer electrolytes (GPEs) are promising candidates to enable safe and room temperature lithium metal (Li°) polymer batteries (LMPBs). Among the different available plasticizers, ionic liquids (ILs) have captured much interest due to their extremely low vapor pressure and high chemical, thermal, and electrochemical stability. Plasticizing polymerized ionic liquid (PIL)-based electrolytes with ILs may lead to intrinsically safe and highly ionically conductive GPEs even at low temperature. Herein, we report the fundamental properties of some representative PIL-based GPEs utilizing sulfonimide anions ([N(SO2RF1)(SO2RF2)]- RF1, RF2 = F or CF3), with the goal to provide a detailed understanding of the diffusion and conduction properties of this intriguing electrolyte family when different anions are involved. Our results suggest that the full bis(fluorosulfonyl)imide (FSI)-based system exhibits higher ionic conductivities and better selectivity in cationic transport as compared to other systems, due to the higher mobility of free ions and the lower content in ion aggregates. It is anticipated that the present work may set the course to design new GPEs rendering an overall improved electrochemical performance.