Solid polymer electrolytes (SPEs) with high ionic conductivity and wide electrochemical window are highly desirable for all-solid-state rechargeable lithium batteries. Herein, we report the use of hydrothermally derived nano-BaTiO3 (BT) as nanofillers in poly(vinyl acetate)/poly(vinylidene fluoride-hexafluoro propylene) and its use as composite SPE (CSPE) for Li-ion batteries. The CSPE was prepared by the solution casting technique and lithium bis-trifluoromethanesulfonylimide is used as salt. The molecular interaction among the various constituents and the surface morphology of the CSPEs were characterized by Fourier-transform infrared spectroscopy and field-emission scanning electron microscopy analysis respectively. BT (7.5 wt %) in CSPE was found to be the optimum composition to obtain a high ion conductivity of 2 × 10-3 S cm-1 at ambient temperature. The CSPE exhibits better mechanical strength (6.9 MPa), wider electrochemical window (5.4 V), and higher lithium transference number (0.48) than SPEs. Solid-state lithium cell was demonstrated as a proof of concept using lithium as an anode and LiFePO4 and SPE/CSPE (7.5 wt % BT) as cathode and electrolyte, respectively. The CSPE cell shows an enhanced specific discharge capacity of 132 mA h g-1 at 0.1 C, cycling performance up to 40 cycles, and 99% coulombic efficiency. The properties above well support the CSPE as a potential electrolyte-cum-separator for Li-ion batteries couple with high-voltage cathode material. © 2018 American Chemical Society.