The high dielectric constant polymer poly (vinylidene fluoride) (PVDF) was blended with PEO-salt polymer electrolytes to improve their ionic conductivity. PVDF did improve the room-temperature ionic conductivity of the polymer electrolytes PEO-LiCF3CO2 and PEO-LiBF4, and the ionic conductivity at room temperature went up one order of magnitude with 10(-5)S/cm for LIB4M-PF4 being the most prominent. PVDF exhibited strong effects on the ionic conductivity and morphology of the polymer electrolytes, such as weakening the association of poly (ethylene oxide) (PEO) with the salt, hindering the formation of the PEO-salt complex, enlarging the crystalline PEO phase in LIAnM-PFm polymer electrolytes, and reducing the crystalline PEO phase in LIBnM-PFm polymer electrolytes. Both LIA4M-PF4 and LIB4M-PF4 polymer electrolytes formed a new PEO-PVDF-salt complex. The new complex in the former was crystalline, but that in the latter was amorphous.