A composite lithium electrolyte composed of polyelectrolyte-grafted nanoparticles and polyethylene glycol dimethyl ether (PEGDME) is synthesized and characterized. Polyanions immobilized by the silica nanoparticles have reduced anion mobility. Composite nanoparticles grafted by poly(lithium 4-styrenesulfonate) only have moderate conductivity at 60 °C. Almost an order increase of the conductivity to ∼10-6 S/cm is achieved by co-polymerization of the poly(ethylene oxide) methacrylate with sodium 4-styrenesulfonate, which enhances dissociation between lithium cation and polyanion and facilitates lithium ion transfer from the inner part of the polyelectrolyte layer. This composite electrolyte has the potential to suppress lithium dendrite growth and enable the use of lithium metal anode in rechargeable batteries.