Poly(arylene ether ketone)-g-poly(vinyl 1-butylimidazolium bis(flouromethyl sulfonyl) host polymer and 1-butyl-1-methylpyrrollidium bis(flouromethane sulfonyl) ionic liquid are synthesized. The host polymer is blended with ionic liquid to prepare the solid electrolyte membrane for lithium secondary battery. The solid electrolyte membranes integrated with ionic liquid show excellent properties in lithium ion conductivity, interfacial resistance, thermal and mechanical stability, depending on the graft chain length. The electrolyte membrane with the longest graft chain shows the highest lithium ion conductivity with the lowest interfacial resistance between electrode and membrane. The charge-discharge profiles are also investigated at various C-rates. The cells fabricated with the electrolyte membrane possessing the longest graft chain show ∼105 mAh g−1 at room temperature under 0.1 °C-rate in the voltage range from 3.8 to 4.2 V.