The effect of nano-sized silica and γ-LiAlO2 on the electrochemical and interfacial properties of P(EO)20LiN(SO2CF2CF3)2–10wt.% filler polymer electrolytes has been studied using linear sweep voltammetry, ac impedance and galvanostatic stripping/deposition on symmetric non-blocking cells. Non-symmetric cells were used to investigate the electrochemical stability window. The limiting current density of the P(EO)20LiBETI polymer electrolytes at 90°C was found to decrease with the addition of nano-sized filler. The presence of silica caused higher interface resistance during storage in open circuit at 90°C. For the galvanostatic Li stripping/deposition at 0.2mA/cm2 at 90°C, the silica containing electrolyte showed the highest initial overvoltage due to the high interface resistance. These results suggest that the presence of nano-size silica in solvent-free P(EO)20LiBETI polymer electrolytes results in no substantial improvement on the electrochemical and interfacial properties of the electrolytes at 90°C.