Dicationic ionic liquids are promising solvents for safe high performance Li-ion battery applications. In this work, we report on the synthesis and characterization of new electrolytes based on geminal dicationic pyrrolidinium and piperidinium bis(trifluoromethane)sulfonimide ionic liquids, where the two cations are linked by variable length oxyethylene chain spacers. All 1 M LiTFSI doped synthesized electrolytes are thermally stable up to 300 °C, and they exhibited remarkable electrochemical stability window up to 6.0 V vs. Li/Li+. Electrolytes were assembled with LiMn2O4 (LMO) spinel in lithium half-cells. Electrochemical cell performance in terms of cyclic voltammetry, rate capability and galvanostatic cycling studies have been studied at 60 °C. Results obtained indicate that both the cationic structure and the length of the oxyethylene chain spacer has a significant influence on the electrochemical performance of LMO-cells. The cell based on the pyrrolidinium electrolyte with the two cationic structures linked by two oxyethylene units exhibit the faster rate capability, with a capacity retention of 45% at 5C, and the highest reversible capacity (ca. 80 mAhg-1).