In the present study, a type of polymer electrolyte (PE) based on a polyacrylonitrile (PAN) polymer network, sulfolane, composite TiO2-SiO2 and vinylene carbonate (VC) as the solid-electrolyte interface (SEI) forming additive were prepared by the casting technique. Liquid electrolyte (LE) was the 1M LiPF6 in sulfolane (TMS). The produced PE and LE working together with the LiFePO4 (LFP) and Li4Ti5O12 (LTO) was characterized by thermal gravimmetry (TG), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charging/discharging. PE had a high ionic conductivity of 9.8×10−4 Scm−1 at 25°C (containing sub-microsize TiO2-SiO2 with vinyl groups of the surface—10% by weight). Charging/discharging capacity of the LFP │LE│LTO system was ca. 150mAhg−1 (VC content 5wt.%) (C/10 rate). This is much higher in comparison to that characteristic of LFP│PE│LTO cell—charging and discharging capacity stabilizes at a value of ca. 120mAhg−1.