We demonstrate the electrochemical performance of a lithium-polymer battery comprising P(VDF-HFP) nanocomposite membrane based gel polymer electrolytes (GPE). The nanocomposite membranes are prepared by incorporating ionic liquid functionalized ZnS nanoparticles on to P(VDF-HFP) copolymer. Soaking the membranes into lithium salt dissolved liquid organic solvents transform them into GPEs. Increasing the nanoparticles content gradually improves the porosity and the solvent uptake capacity of the membrane. The optimized membrane with 64% porosity shows highest electrolyte uptake ability of 89% to form a flame-retardant GPE endowing a maximum ionic conductivity of 3.3 mS cm−1 at ambient temperature along with an excellent lithium ion transfer number of 0.62. The cell comprising the optimized GPE with LiFePO4 cathode and Li metal anode shows outstanding electrochemical performance at ambient temperature, delivering a discharge capacity of ∼161 mAh/g at C/10 rate and able to retain its 89% after 50 cycles. The study suggests that conjoining ionic liquid tethered nanoparticles with insulating polymers provides a promising way to produce efficient active polymer membranes based high-performance GPEs, enabling safer, high energy density, lithium-polymer batteries.