In this work, we report novel room temperature ionic liquid (RTIL)-based electrolytes to be used with high-energy cathode, lithium-rich nickel manganese cobalt oxide (Li[Li0.2Mn0.56Ni0.16Co0.08]O2, LiR-NMC) in Li-ion batteries. The physical and electrochemical characteristics of the newly developed materials are thoroughly detailed, also by means of post-cycling electrochemical impedance spectroscopy (EIS) analysis of the resulting lab-scale lithium cells upon long-term, constant-current cycling (>1200 cycles). In addition, an innovative polymer electrolyte is developed encompassing the best performing RTIL-based electrolyte mixture, which is investigated in terms of its physico-chemical features, ion transport and electrochemical behaviour by EIS, cyclic voltammetry and constant-current (galvanostatic) cycling. The polymer electrolyte is obtained via facile, rapid and easily up-scalable UV-induced free radical polymerization (UV curing) technique, being a low-cost and solvent-free approach compared to other existing film formation techniques. The versatile fabrication method along with the use of appropriate materials may turn high-voltage, solid state and ageing resistant batteries into industrial reality in the coming years, as underlined by the excellent electrochemical response of the lithium polymer cell.