We report a family of flame-retardant electrolytes for lithium batteries based on ionic nanocomposites. The nanocomposites are synthesized in one pot by dispersing SiO2 nanoparticles charge-balanced by both Li ions and mono-amino-terminated polyether (PEO-b-PPO-NH3 +) in an oligomeric PEO matrix. The Li+ and PEO-b-PPO-NH3 + ions lead to enhanced Li+ transference number and compatibility with the PEO matrix, respectively. The nanocomposite electrolyte containing 40% mass fraction of silica shows a notable electrochemical stability window of more than 6 V in contact with Lithium and high Li+ transference number over 0.5. Rheology measurements demonstrate the tunability of the system from liquid to gel-like as the silica mass fraction percentage increases from 0 to 40% while the conductivity remains almost constant. Thermal gravimetric and microscale combustion calorimeter measurements of the nanocomposites show decreased rate of mass loss and heat release rate compared to neat electrolyte. Finally, the fire retardancy of the nanocomposites measured by directly observing the formation and sustainability of flame, when exposed to direct fire, make them promising candidates in the ever-growing quest for safe lithium batteries.